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{{Short description|Circumstances, mechanisms, and factors of tobacco consumption on human health}}
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{{redirect-multi|2|Health effects of smoking|Dangers of smoking|cannabis|Effects of cannabis|smoking crack cocaine|Crack cocaine#Health issues}}

[[File:Risks form smoking-smoking can damage every part of the body.png|thumb|upright=1.4|A diagram of the human body showing cancers and chronic diseases caused by smoking]] 
[[Tobacco]] use has predominantly negative effects on human health and concern about '''health effects of tobacco''' has a long history. Research has focused primarily on [[cigarette]] smoking.<ref name="WHOPrevalenceAdultsAge15"/><ref name="WHOMayoReport"/>

Tobacco smoke contains more than [[list of cigarette smoke carcinogens|70 chemicals]] that [[carcinogen|cause cancer]].<ref name=WHO2014/> Tobacco also contains [[nicotine]], which is a highly [[addiction|addictive]] [[psychoactive drug]]. When tobacco is smoked, nicotine causes physical and [[psychological dependency]]. Cigarettes sold in [[Underdeveloped country|underdeveloped countries]] tend to have higher tar content, and are less likely to be filtered, potentially increasing vulnerability to tobacco smoking–related disease in these regions.<ref name = "Nichter_1991">{{cite journal | jstor = 648675 | doi = 10.1525/maq.1991.5.3.02a00040 | title = Saving the Children for the Tobacco Industry | year =1991 | vauthors = Nichter M, Cartwright E | journal = Medical Anthropology Quarterly | volume = 5 | issue = 3 | pages = 236–56 }}</ref>

Tobacco use is the single greatest [[preventable cause of death|cause of preventable death]] globally.<ref name="isbn92-4-159628-7">{{Cite book |date=2008 |title=WHO Report on the Global Tobacco Epidemic 2008 : The MPOWER Package. |url=https://apps.who.int/iris/bitstream/handle/10665/43818/9789241596282_eng.pdf?sequence=1&isAllowed=y |archive-url=https://web.archive.org/web/20220121162003/https://apps.who.int/iris/bitstream/handle/10665/43818/9789241596282_eng.pdf?sequence=1&isAllowed=y |archive-date=1 January 2022 |access-date=2022-10-06 |publisher=[[World Health Organization]] |pages=6, 8, 20 |isbn=9789240683112 |oclc=476167599}}</ref> As many as half of people who use tobacco die from complications of tobacco use.<ref name=WHO2014>{{cite web|title=Tobacco Fact sheet N°339|url=https://www.who.int/mediacentre/factsheets/fs339/en/|access-date=13 May 2015|date=May 2014}}</ref> The [[World Health Organization]] (WHO) estimates that each year tobacco causes about 6 million deaths (about 10% of all deaths) with 600,000 of these occurring in non-smokers due to [[second-hand smoke]].<ref name=WHO2014/><ref>{{cite web|title=The top 10 causes of death|url=https://www.who.int/mediacentre/factsheets/fs310/en/index2.html|archive-url=https://web.archive.org/web/20070314013115/http://www.who.int/mediacentre/factsheets/fs310/en/index2.html|url-status=dead|archive-date=March 14, 2007|access-date=13 May 2015}}</ref> Tobacco is estimated to have caused 100 million deaths in the 20th century.<ref name=WHO2014/> Similarly, the United States [[Centers for Disease Control and Prevention]] describes tobacco use as "the single most important preventable risk to human health in developed countries and an important cause of premature death worldwide."<ref name="fn1">"[https://www.cdc.gov/tobacco/quit_smoking/you_can_quit/nicotine.htm Nicotine: A Powerful Addiction] {{webarchive|url=https://web.archive.org/web/20090501011931/http://www.cdc.gov/tobacco/quit_smoking/you_can_quit/nicotine.htm |date=2009-05-01 }}." Centers for Disease Control and Prevention.</ref> Currently, the number of premature deaths in the U.S. from tobacco use per year outnumber the number of workers employed in the tobacco industry by 4 to 1.<ref>{{Cite web|url=https://www.iflscience.com/editors-blog/these-two-industries-kill-more-people-than-they-employ/|title=These Two Industries Kill More People Than They Employ|website=IFLScience|access-date=2019-03-09}}</ref> According to a 2014 review in ''[[The New England Journal of Medicine]]'', tobacco will kill about 1 billion people in the 21st century if current smoking patterns persist, half of them before the age of 70.<ref>{{cite journal | vauthors = Jha P, Peto R | title = Global effects of smoking, of quitting, and of taxing tobacco | journal = The New England Journal of Medicine | volume = 370 | issue = 1 | pages = 60–8 | date = January 2014 | pmid = 24382066 | doi = 10.1056/nejmra1308383 | s2cid = 4299113 | url = https://semanticscholar.org/paper/83fbcac3e5d959923397aaa07317a14c852b4948 }}</ref>

China has largest tobacco smoking population, followed by [[India]]. India has highest tobacco chewing population in the world. 154 people die every hour in India due to tobacco.<ref>{{cite news |last1=Dubey |first1=Divyani |title=Data Dive: Tobacco Kills 3,700 People Every Day, Causes 27% of Cancer Cases |url=https://www.factchecker.in/data-dive/data-dive-tobacco-kills-3700-people-every-day-causes-27-of-cancer-cases-820260 |access-date=2022-09-04 |work=Factchecker.in |date=2022-06-01}}</ref><ref>{{cite web |title=Tobacco in China |url=https://www.who.int/china/health-topics/tobacco |website=World Health Organization |publisher=[[World Health Organization]] |access-date=2022-09-04 |archive-url=https://web.archive.org/web/20220803193309/https://www.who.int/china/health-topics/tobacco |archive-date=2022-08-03}}</ref>

<!-- Morbidity -->
Tobacco use most commonly leads to [[Cardiovascular disease|diseases affecting the heart]], [[Liver disease|liver]] and [[Respiratory disease|lungs]]. Smoking is a major [[risk factor]] for infections like [[pneumonia]], [[myocardial infarction|heart attacks]], [[stroke]]s, [[chronic obstructive pulmonary disease]] (COPD) (including [[emphysema]] and [[Bronchitis#Chronic bronchitis|chronic bronchitis]]), and multiple [[cancer]]s (particularly [[lung cancer]], [[Laryngeal cancer|cancers of the larynx and mouth]], [[bladder cancer]], and [[pancreatic cancer]]). It also causes [[peripheral arterial disease]] and [[hypertension|high blood pressure]]. The effects depend on the number of years that a person smokes and on how much the person smokes. Starting smoking earlier in life and smoking cigarettes higher in [[Tar (tobacco residue)|tar]] increases the risk of these diseases. Also, environmental tobacco smoke, or second-hand smoke, has been shown to cause adverse health effects in people of all ages.<ref name="pmid3303311">{{cite journal | vauthors = Vainio H | title = Is passive smoking increasing cancer risk? | journal = Scandinavian Journal of Work, Environment & Health | volume = 13 | issue = 3 | pages = 193–6 | date = June 1987 | pmid = 3303311 | doi = 10.5271/sjweh.2066 | doi-access = free }}</ref> Tobacco use is a significant factor in [[Spontaneous abortion|miscarriages]] among [[Smoking and pregnancy|pregnant smokers]], and it contributes to a number of other health problems of the [[fetus]] such as [[premature birth]], [[low birth weight]], and increases by 1.4 to 3 times the chance of [[sudden infant death syndrome]] (SIDS).<ref name="SurgeonGeneralPassiveSmoking2006">{{cite web|url=http://www.surgeongeneral.gov/library/secondhandsmoke/report/fullreport.pdf|title=The health consequences of involuntary exposure to tobacco smoke: a report of the Surgeon General|access-date=2009-02-15|year=2006|publisher=U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Chronic Disease Prevention and Health Promotion, Office on Smoking and Health|location=Atlanta, U.S. | page = 93 }}</ref> Incidence of [[erectile dysfunction]] is approximately 85 percent higher in male smokers compared to non-smokers.<ref name=pmid15924009/><ref name=pmid15146084>{{cite journal | vauthors = Korenman SG | title = Epidemiology of erectile dysfunction | journal = Endocrine | volume = 23 | issue = 2–3 | pages = 87–91 | year = 2004 | pmid = 15146084 | doi = 10.1385/ENDO:23:2-3:087 | s2cid = 29133230 }}</ref>

<!-- Prevention -->
Several countries have taken measures to control the consumption of tobacco with usage and sales restrictions as well as [[Tobacco packaging warning messages|warning messages]] printed on packaging. Additionally, [[smoke-free laws]] that ban smoking in public places such as workplaces, theaters, and bars and restaurants have been enacted to reduce exposure to second-hand smoke.<ref name=WHO2014/> [[Tobacco taxes]] that increase the price of tobacco products have also been enacted.<ref name=WHO2014/>

<!-- History -->
In the late 1700s and the 1800s, the idea that tobacco use caused some diseases, including mouth cancers, was initially widely accepted by the medical community.<ref name=dolls_history/> In the 1880s, automation dramatically reduced the cost of cigarettes, tobacco companies greatly increased their marketing, and use expanded.<ref name=early_prohibition>{{Cite journal| volume = 39| issue = 4| pages = 425–445| vauthors = Alston LJ, Dupré R, Nonnenmacher T | title = Social reformers and regulation: the prohibition of cigarettes in the United States and Canada| journal = Explorations in Economic History| date = 2002| doi = 10.1016/S0014-4983(02)00005-0}}</ref><ref name=time_advertising>{{cite magazine| vauthors = James R |url= http://www.time.com/time/magazine/article/0,9171,1905530,00.html |archive-url= https://web.archive.org/web/20110921054816/http://www.time.com/time/magazine/article/0,9171,1905530,00.html |url-status= dead |archive-date= September 21, 2011 |title=A Brief History Of Cigarette Advertising |magazine=TIME |date=2009-06-15 |access-date=2012-03-25}}</ref> From the 1890s onwards, associations of tobacco use with cancers and [[vascular disease]] were regularly reported; a [[meta-analysis]] citing 167 other works was published in 1930, and concluded that tobacco use caused cancer.<ref name=Lickint_bio/><ref name="about_lickint"/><!-- the one source says 1929, the other 1930; 1929 seems to be a typo, as the source cited for it says 1930, and the Lickint review is dated 1930 --> Increasingly solid observational evidence was published throughout the 1930s, and in 1938, ''[[Science (journal)|Science]]'' published a paper showing that tobacco users live substantially shorter lives. Case-control studies were published in [[Nazi Germany]] in 1939 and 1943, and one in the Netherlands in 1948, but widespread attention was first drawn by five case-control studies published in 1950 by researchers from the US and UK. These studies were widely criticized as showing [[correlation, not causality]]. Follow-up [[Prospective cohort study|prospective cohort studies]] in the early 1950s clearly found that smokers died faster, and were more likely to die of [[lung cancer]] and [[cardiovascular disease]].<ref name=dolls_history/> These results were first widely accepted in the medical community, and publicized among the general public, in the mid-1960s.<ref name=dolls_history/>

{{Tobacco}}

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== History ==

===Pre-cigarette===
Concern about health effects of tobacco has a long history. The coughing, throat irritation, and shortness of breath caused by smoking have always been obvious.{{citation needed|date=August 2018}}

Texts on the harmful effects of smoking tobacco were recorded in the [[Timbuktu manuscripts]].<ref>Djian, Jean-Michel (24 May 2007). [http://portal.unesco.org/en/ev.php-URL_ID=37896&URL_DO=DO_PRINTPAGE&URL_SECTION=201.html Timbuktu manuscripts: Africa's written history unveiled] {{Webarchive|url=https://web.archive.org/web/20091111190441/http://portal.unesco.org/en/ev.php-URL_ID%3D37896%26URL_DO%3DDO_PRINTPAGE%26URL_SECTION%3D201.html |date=11 November 2009 }}. Unesco, ID 37896.</ref>

[[Pipe smoking]] gradually became generally accepted as a cause of mouth cancers following work done in the 1700s. "An association between a variety of cancers and tobacco use was repeatedly observed from the late 1800s into the early 1920s."<ref>{{Cite journal |last=Brandt |first=Allan M. |date=January 2012 |title=Inventing Conflicts of Interest: A History of Tobacco Industry Tactics |journal=American Journal of Public Health |volume=102 |issue=1 |pages=63–71 |doi=10.2105/AJPH.2011.300292 |issn=0090-0036 |pmc=3490543 |pmid=22095331}}</ref>

[[Gideon Lincecum]], an American naturalist and practitioner of botanical medicine, wrote in the early 19th century on tobacco: "This poisonous plant has been used a great deal as a medicine by the old school faculty, and thousands have been slain by it. ... It is a very dangerous article, and use it as you will, it always diminishes the vital energies in exact proportion to the quantity used – it may be slowly, but it is very sure."<ref>{{cite web| vauthors = Lincecum G |title=Nicotiana tabacum|url=http://w3.biosci.utexas.edu/prc/lincecum/pages/Nicotiana_tabacum-notes.html|work=Giden Lincecum Herbarium|publisher=University of Texas|access-date=9 December 2012}}</ref>

The 1880s invention of automated cigarette-making machinery in the American South made it possible to mass-produce cigarettes at low cost, and smoking became common. This led to a backlash and a tobacco prohibition movement, which challenged tobacco use as harmful and brought about some bans on tobacco sale and use.<ref name=early_prohibition/> In 1912, American Dr. Isaac Adler was the first to strongly suggest that lung cancer is related to smoking.<ref name="pmid6773624">{{cite journal | vauthors = Adler IA | title = Classics in oncology. Primary malignant growths of the lung. Isaac A. Adler, A.M., M.D | journal = CA: A Cancer Journal for Clinicians | volume = 30 | issue = 5 | pages = 295–301 | year = 1980 | pmid = 6773624 | doi = 10.3322/canjclin.30.5.295 | s2cid = 6967224 | doi-access = free }}</ref> In 1924, economist [[Irving Fisher]] wrote an [[anti-smoking]] article for ''[[Reader's Digest]]'' which said "...tobacco lowers the whole tone of the body and decreases its vital power and resistance ... tobacco acts like a narcotic poison, like opium, and like alcohol, though usually in a less degree".<ref>{{cite web |url=http://legacy.library.ucsf.edu/tid/fgo81c00/pdf;jsessionid=512902F957843008C40E997C9D0B9A6C.tobacco03 |title=Does tobacco injure the human body? | vauthors = Fisher I |year=1924 |work=Reader's Digest |url-status=dead |archive-url=https://web.archive.org/web/20140418233913/http://legacy.library.ucsf.edu/tid/fgo81c00/pdf%3Bjsessionid%3D512902F957843008C40E997C9D0B9A6C.tobacco03 |archive-date=2014-04-18 }}</ref>{{Non sequitur|reason=What is the relevance of this to anything, especially a quote from a non-expert conflating narcotics (not the modern LEO term, the proper medical one) with alcohol and cigarettes with either of the two.  A person can do opium, drink, and smoke, and probably be healthier than someone who sits around worrying about other peoples' money and writing uneducated screeds on their spare-time activities...|date=April 2021}} ''In December 1952, the Reader's Digest'' reprinted an article titled [https://csts.ua.edu/files/2019/01/1952-12-Readers-Digest-Cancer-by-the-Carton.pdf Cancer by the Carton] which outlined the research links between smoking and lung cancer.

Prior to [[World War I]], lung cancer was considered to be a rare disease, which most physicians would never see during their career.<ref name="Cite pmid|11606795">{{cite journal | vauthors = Witschi H | title = A short history of lung cancer | journal = Toxicological Sciences | volume = 64 | issue = 1 | pages = 4–6 | date = November 2001 | pmid = 11606795 | doi = 10.1093/toxsci/64.1.4 | doi-access = free }}</ref><ref>{{cite book | vauthors = Adler I | title = Primary malignant growths of the lungs and bronchi: a pathological and clinical study | location = New York | publisher = Longmans, Green | year = 1912 | oclc = 14783544 | url = https://books.google.com/books?id=SucRAAAAYAAJ}}{{Page needed|date=November 2010}}, cited in {{cite journal | vauthors = Spiro SG, Silvestri GA | title = One hundred years of lung cancer | journal = American Journal of Respiratory and Critical Care Medicine | volume = 172 | issue = 5 | pages = 523–9 | date = September 2005 | pmid = 15961694 | doi = 10.1164/rccm.200504-531OE | s2cid = 21653414 | url = https://semanticscholar.org/paper/0bb2970c8d7fc657acb0893366fb42f6af2b9780 }}</ref> With the postwar rise in popularity of cigarette smoking, however, came an epidemic of lung cancer.<ref>{{cite web | title = 20 Year Lag Time Between Smoking and Lung Cancer | author = National Cancer Institute | url-status = dead | url = http://press2.nci.nih.gov/sciencebehind/cancer/cancer31.htm | archive-url = https://web.archive.org/web/20030217151857/http://press2.nci.nih.gov/sciencebehind/cancer/cancer31.htm | archive-date = 17 February 2003 }}</ref><ref>{{Cite journal|last=Proctor|first=Robert N.|date=May 2004|title=The Global Smoking Epidemic: A History and Status Report|url=https://linkinghub.elsevier.com/retrieve/pii/S1525730411701899|journal=Clinical Lung Cancer|language=en|volume=5|issue=6|pages=371–376|doi=10.3816/CLC.2004.n.016|pmid=15217537}}</ref>{{Additional citation needed|reason=One might also correlate the sudden rapid increase in the 40s with the advent of open-air nuclear bomb testing, but nobody likes to talk about that and they probably weren't testing radionuclide levels in lungs of cancer victims.  Something that bothers to account for this might be helpful.|date=April 2021}} For instance, it is estimated that "35 to 79 percent of excess veteran deaths due to heart disease and lung cancer are attributable to military-induced smoking"<ref>{{Cite journal|last1=Bedard|first1=Kelly|last2=Deschênes|first2=Olivier|date=2006-02-01|title=The Long-Term Impact of Military Service on Health: Evidence from World War II and Korean War Veterans|url=https://pubs.aeaweb.org/doi/10.1257/000282806776157731|journal=American Economic Review|language=en|volume=96|issue=1|pages=176–194|doi=10.1257/000282806776157731|pmid=29125728|issn=0002-8282}}</ref>

===Early observational studies===
From the 1890s onwards, associations of tobacco use with cancers and vascular disease were regularly reported.<ref name=dolls_history/> In 1930, [[Fritz Lickint]] of [[Dresden]], [[Germany]], published<ref name="about_lickint">{{cite journal | vauthors = Proctor RN | title = Commentary: Schairer and Schöniger's forgotten tobacco epidemiology and the Nazi quest for racial purity | journal = International Journal of Epidemiology | volume = 30 | issue = 1 | pages = 31–4 | date = February 2001 | pmid = 11171846 | doi = 10.1093/ije/30.1.31 | doi-access = free }}</ref><ref name=Lickint_bio/><!-- the one source says 1929, the other 1930; 1929 seems to be a typo, as the source cited for it says 1930, and the Lickint review, "Tabak und Tabakrauch als ätiologischer Faktor des Carcinoms" is dated 1930 --> a [[metaanalysis]] citing 167 other works to link tobacco use to lung cancer.<ref name=Lickint_bio>{{cite journal| vauthors = Haustein KO |year=2004|title=Fritz Lickint (1898–1960) – Ein Leben als Aufklärer über die Gefahren des Tabaks|journal=Suchtmed |volume=6|issue=3|pages=249–255|url=http://www.ecomed-medizin.de/sj/sfp/Pdf/aId/6824 |archive-url= https://web.archive.org/web/20141105152951/http://www.ecomed-medizin.de/sj/sfp/Pdf/aId/6824 |archive-date= November 5, 2014 |language=de}}</ref> Lickint showed that people with [[lung cancer]]  were likely to be smokers. He also argued that tobacco use was the best way to explain the fact that lung cancer struck men four or five times more often than women (since women smoked much less),<ref name=about_lickint /> and discussed the causal effect of smoking on cancers of the liver and bladder.<ref name=Lickint_bio/>

{{quotebox|align=right|width=35%|It may be suggested that the chief reason that the subject has received so little attention from members of the medical profession is that the majority of them as of the general community practice smoking in one form of another, and do not wish to inquire too closely into a habit in defense of which so much can be said from the hedonistic but so little from the hygienic standpoint|source={{Cite journal| doi = 10.1111/j.1360-0443.1932.tb04849.x | volume = 30| issue = 1| pages = 1–27| vauthors = Rolleston JD | title = The Cigarette Habit| journal = Addiction| date = July 1932| s2cid = 72586449}} }}

More observational evidence was published throughout the 1930s, and in 1938, ''[[Science (journal)|Science]]'' published a paper showing that tobacco users live substantially shorter lives. It built a [[survival curve]] from family history records kept at the [[Johns Hopkins School of Hygiene and Public Health]]. This result was ignored or incorrectly explained away.<ref name=dolls_history/>

An association between tobacco and heart attacks was first mentioned in 1930; a large [[case–control study]] found a significant association in 1940, but avoided saying anything about cause, on the grounds that such a conclusion would cause controversy and doctors were not yet ready for it.<ref name=dolls_history>{{cite journal | vauthors = Doll R | title = Uncovering the effects of smoking: historical perspective | journal = Statistical Methods in Medical Research | volume = 7 | issue = 2 | pages = 87–117 | date = June 1998 | pmid = 9654637 | doi = 10.1177/096228029800700202 | s2cid = 154707 | url = http://www.toxicology.usu.edu/endnote/doll-effects-of-smoking-smmr-7-87-1998.pdf | access-date = 2018-09-30 | archive-url = https://web.archive.org/web/20181001070108/http://www.toxicology.usu.edu/endnote/doll-effects-of-smoking-smmr-7-87-1998.pdf | archive-date = 2018-10-01 | url-status = dead }}</ref>

{{see also|Institute for the Struggle against the Dangers of Tobacco}}
[[Anti-tobacco movement in Nazi Germany|Official hostility]] to tobacco use was widespread in Nazi Germany where case-control studies were published in 1939 and 1943. Another was published in the Netherlands in 1948. A case-control study on lung cancer and smoking, done in 1939 by [[Franz Hermann Müller]], had serious weaknesses in its methodology, but study design problems were better addressed in subsequent studies.<ref name=dolls_history/> The association of anti-tobacco research and public health measures with the Nazi leadership may have contributed to the lack of attention paid to these studies.<ref name="about_lickint"/> They were also published in German and Dutch. These studies were widely ignored.<ref name="isbn1-59691-610-9">{{cite book | vauthors = [[Naomi Oreskes|Oreskes N]], Conway EM | title = Merchants of Doubt: How a Handful of Scientists Obscured the Truth on Issues from Tobacco Smoke to Global Warming | publisher = Bloomsbury Press | location = San Francisco, CA | year = 2010 | page = [https://archive.org/details/merchantsofdoubt00ores/page/15 15] | isbn = 978-1-59691-610-4 | title-link = Merchants of Doubt }}</ref> In 1947 the British Medical Council held a conference to discuss the reason for the rise in lung cancer deaths; unaware of the German studies, they planned and started their own.<ref name=dolls_history/>

Five case-control studies published in 1950 by researchers from the US and UK did draw widespread attention.<ref name="isbn0-19-530067-X"/> The strongest results were found by "Smoking and carcinoma of the lung. Preliminary report", by [[Richard Doll]] and [[Austin Bradford Hill]],<ref name="Cite pmid|14772469"/><ref name=dolls_history/> and the [[1950 Wynder and Graham Study]], entitled "Tobacco Smoking as a Possible Etiologic Factor in Bronchiogenic Carcinoma: A Study of Six Hundred and Eighty-Four Proved Cases". These two studies were the largest, and the only ones to carefully exclude ex-smokers from their nonsmokers group. The other three studies also reported that, to quote one, "smoking was powerfully implicated in the causation of lung cancer".<ref name="isbn0-19-530067-X"/> The Doll and Hill paper reported that "heavy smokers were fifty times as likely as non-smokers to contract lung cancer".<ref name="Cite pmid|14772469">{{cite journal | vauthors = Doll R, Hill AB | title = Smoking and carcinoma of the lung; preliminary report | journal = British Medical Journal | volume = 2 | issue = 4682 | pages = 739–48 | date = September 1950 | pmid = 14772469 | pmc = 2038856 | doi = 10.1136/bmj.2.4682.739 }}</ref><ref name="isbn0-19-530067-X">{{cite book | vauthors = Michaels D | title = Doubt is their product: how industry's assault on science threatens your health | publisher = Oxford University Press | location = Oxford [Oxfordshire] | year = 2008 | pages = [https://archive.org/details/doubtistheirprod00mich/page/4 4–5] | isbn = 978-0-19-530067-3 | url = https://archive.org/details/doubtistheirprod00mich/page/4 }}</ref>

===Causality===
The case-control studies clearly showed a close link between smoking and [[lung cancer]], but were criticized for not showing [[causality]]. Follow-up large [[prospective cohort studies]] in the early 1950s showed clearly that smokers died faster, and were more likely to die of lung cancer, [[cardiovascular disease]], and a list of other diseases which lengthened as the studies continued<ref name=dolls_history/>

The [[British Doctors Study]], a [[longitudinal study]] of some 40,000 doctors, began in 1951.<ref name="Doll_2004"/> By 1954 it had evidence from three years of doctors' deaths, based on which the government issued advice that smoking and lung cancer rates were related<ref name="pmid15217868">{{cite journal | vauthors = Doll R, Hill AB | title = The mortality of doctors in relation to their smoking habits: a preliminary report. 1954 | journal = BMJ | volume = 328 | issue = 7455 | pages = 1529–33; discussion 1533 | date = June 2004 | pmid = 15217868 | pmc = 437141 | doi = 10.1136/bmj.328.7455.1529 }}</ref><ref name="Doll_2004">{{cite journal | vauthors = Doll R, Peto R, Boreham J, Sutherland I | title = Mortality in relation to smoking: 50 years' observations on male British doctors | journal = BMJ | volume = 328 | issue = 7455 | pages = 1519 | date = June 2004 | pmid = 15213107 | pmc = 437139 | doi = 10.1136/bmj.38142.554479.AE }}</ref> (the British Doctors Study last reported in 2001,<ref name="Doll_2004"/> by which time there were approximately 40 linked diseases).<ref name=dolls_history/> The British Doctors Study demonstrated that about half of the persistent cigarette smokers born in 1900–1909 were eventually killed by their addiction<ref>{{Cite journal|last1=Di Cicco|first1=Maria Elisa|last2=Ragazzo|first2=Vincenzo|last3=Jacinto|first3=Tiago|date=September 2016|title=Mortality in relation to smoking: the British Doctors Study|journal=Breathe|language=en|volume=12|issue=3|pages=275–276|doi=10.1183/20734735.013416|issn=1810-6838|pmc=5298160|pmid=28210302}}</ref> (calculated from the [[logarithm]]s of the probabilities of surviving from 35 to 70, 70–80, and 80–90) and about two thirds of the persistent cigarette smokers born in the 1920s would eventually be killed by their addiction.{{citation needed|date=October 2016}}

===Public awareness===
In 1953, scientists at the [[Memorial Sloan–Kettering Cancer Center|Sloan-Kettering Institute]] in New York City demonstrated that cigarette tar painted on the skin of mice caused fatal cancers.<ref name="isbn1-59691-610-9"/> This work attracted much media attention; the ''New York Times'' and ''Life'' both covered the issue. The ''Reader's Digest'' published an article entitled "Cancer by the Carton".<ref name="isbn1-59691-610-9"/>{{RP|14}}

On January 11, 1964, the United States [[Surgeon General of the United States|Surgeon General]]'s [[Smoking and Health: Report of the Advisory Committee to the Surgeon General of the United States|Report on Smoking and Health]] was published; this led millions of American smokers to quit, the banning of certain advertising, and the requirement of warning labels on tobacco products.<ref name="1964 full report">{{Cite report |url=https://profiles.nlm.nih.gov/spotlight/nn/catalog/nlm:nlmuid-101584932X202-doc# |title=Smoking and Health: Report of the Advisory Committee to the Surgeon General of the United States |last=[[Surgeon General of the United States]] |date=1964 |publisher=[[United States Department of Health and Human Services|Department of Health, Education, and Welfare]] |id=Public Health Service Publication No. 1103 |archive-url=https://web.archive.org/web/20220728033124/https://www.govinfo.gov/content/pkg/GPO-SMOKINGANDHEALTH/pdf/GPO-SMOKINGANDHEALTH.pdf |archive-date=28 July 2022}}</ref><ref name="64 review">{{Cite journal |last1=Chapman |first1=Simon |last2=MacKenzie |first2=Ross |date=February 9, 2010 |title=The Global Research Neglect of Unassisted Smoking Cessation: Causes and Consequences |journal=[[PLOS Medicine]] |volume=7 |issue=2 |pages=e1000216 |doi=10.1371/journal.pmed.1000216 |pmc=2817714 |pmid=20161722}}</ref>

These results were first widely accepted in the medical community, and publicized among the general public, in the mid-1960s.<ref name=dolls_history/> The medical community's resistance to the idea that tobacco caused disease has been attributed to bias from nicotine-dependent doctors, the novelty of the adaptations needed to apply epidemiological techniques and heuristics to non-infectious diseases, and tobacco industry pressure.<ref name=dolls_history/>

The health effects of smoking have been significant for the development of the science of [[epidemiology]]. As the mechanism of carcinogenicity is radiomimetic or radiological, the effects are [[stochastic]]. Definite statements can be made only on the relative increased or decreased probabilities of contracting a given disease. For a particular individual, it is impossible to definitively prove a direct causal link between exposure to a radiomimetic poison such as tobacco smoke and the cancer that follows; such statements can only be made at the aggregate population level. Tobacco companies have capitalized on this philosophical objection and exploited the doubts of clinicians, who consider only individual cases, on the causal link in the stochastic expression of the toxicity as actual disease.<ref name="isbn0-465-07047-7">{{cite book | vauthors = Brandt AM | title = The cigarette century: the rise, fall and deadly persistence of the product that defined America | publisher = Basic Books, a member of the Perseus Books Group | location = New York | year = 2007 | isbn = 978-0-465-07047-3 | url = https://archive.org/details/cigarettecentury00bran }}</ref>

There have been multiple court cases against tobacco companies for having researched the health effects of tobacco, but having then suppressed the findings or formatted them to imply lessened or no hazard.<ref name="isbn0-465-07047-7"/>

After a ban on smoking in all enclosed public places was introduced in Scotland in March 2006, there was a 17 percent reduction{{when|date=June 2016}} in hospital admissions for acute coronary syndrome. 67% of the decrease occurred in non-smokers.<ref name="pell jp1">{{cite journal | vauthors = Pell JP, Haw S, Cobbe S, Newby DE, Pell AC, Fischbacher C, McConnachie A, Pringle S, Murdoch D, Dunn F, Oldroyd K, Macintyre P, O'Rourke B, Borland W | title = Smoke-free legislation and hospitalizations for acute coronary syndrome | journal = The New England Journal of Medicine | volume = 359 | issue = 5 | pages = 482–91 | date = July 2008 | pmid = 18669427 | doi = 10.1056/NEJMsa0706740 | first8 = S. | hdl = 1893/16659 | url = http://dspace.stir.ac.uk/bitstream/1893/16659/1/Haw_Smoke_free_legislation_and_hospitalisations_acute_coronary_syndrome.pdf }}</ref>

== Health effects of smoking ==
[[File:Rational harm assessment of drugs radar plot.svg|thumb|Addiction experts in psychiatry, chemistry, pharmacology, forensic science, epidemiology, and the police and legal services engaged in [[Delphi method|delphic analysis]] regarding 20 popular recreational drugs. Tobacco was ranked 3rd in dependence, 14th in physical harm, and 12th in social harm.<ref>{{cite journal | vauthors = Nutt D, King LA, Saulsbury W, Blakemore C | title = Development of a rational scale to assess the harm of drugs of potential misuse | journal = Lancet | volume = 369 | issue = 9566 | pages = 1047–53 | date = March 2007 | pmid = 17382831 | doi = 10.1016/s0140-6736(07)60464-4 | s2cid = 5903121 }}</ref>]]
Smoking most commonly leads to diseases affecting the heart and [[respiratory system|lungs]] and will commonly affect areas such as hands or feet. First signs of smoking-related health issues often show up as numbness in the extremities, with smoking being a major risk factor for [[myocardial infarction|heart attacks]], [[chronic obstructive pulmonary disease]] (COPD), [[emphysema]], and [[cancer]], particularly [[lung cancer]], cancers of the [[larynx]] and [[mouth]], and [[pancreatic cancer]].<ref>{{cite web|url=http://betobaccofree.hhs.gov/health-effects/index.html|title=Health Effects of Tobacco|author=ASPA|access-date=8 September 2014|archive-url=https://web.archive.org/web/20140920224920/http://betobaccofree.hhs.gov/health-effects/index.html|archive-date=2014-09-20|url-status=dead}}</ref> Overall life expectancy is also reduced in long term smokers, with estimates ranging from 10<ref name="Doll_2004"/> to 17.9<ref name="urlLife Expectancy at Age 30: Nonsmoking Versus Smoking Men">{{cite web | url = http://tobaccodocuments.org/ti/TIMN0020615-0620.html | title = Life Expectancy at Age 30: Nonsmoking Versus Smoking Men | publisher = Tobacco Documents Online | access-date = 2012-05-06 | url-status = dead | archive-url = https://web.archive.org/web/20120419010343/http://tobaccodocuments.org/ti/TIMN0020615-0620.html | archive-date = 2012-04-19 }}</ref> years fewer than nonsmokers.<ref name="pmid10192312">{{cite journal | vauthors = Ferrucci L, Izmirlian G, Leveille S, Phillips CL, Corti MC, Brock DB, Guralnik JM | title = Smoking, physical activity, and active life expectancy | journal = American Journal of Epidemiology | volume = 149 | issue = 7 | pages = 645–53 | date = April 1999 | pmid = 10192312 | doi = 10.1093/oxfordjournals.aje.a009865 | doi-access = free }}</ref> About one half of long term male smokers will die of illness due to smoking.<ref name="pmid7755693">{{cite journal | vauthors = Doll R, Peto R, Wheatley K, Gray R, Sutherland I | title = Mortality in relation to smoking: 40 years' observations on male British doctors | journal = BMJ | volume = 309 | issue = 6959 | pages = 901–11 | date = October 1994 | pmid = 7755693 | pmc = 2541142 | doi = 10.1136/bmj.309.6959.901 }}</ref> The association of smoking with lung cancer is strongest, both in the public perception and etiologically. Among male smokers, the lifetime risk of developing lung cancer is 17.2%; among female smokers, the risk is 11.6%. This risk is significantly lower in nonsmokers: 1.3% in men and 1.4% in women.<ref name="pmid7895211">{{cite journal | vauthors = Villeneuve PJ, Mao Y | title = Lifetime probability of developing lung cancer, by smoking status, Canada | journal = Canadian Journal of Public Health | volume = 85 | issue = 6 | pages = 385–8 | year = 1994 | pmid = 7895211 }}</ref>

A person's increased [[risk]] of contracting disease is related to the length of time that a person continues to smoke as well as the amount smoked. However, even smoking one cigarette a day raises the risk of [[coronary heart disease]] by about 50% or more, and for [[stroke]] by about 30%. Smoking 20 cigarettes a day entails a higher risk, but not proportionately.<ref>{{cite journal | vauthors = Johnson K |title=Just one cigarette a day seriously elevates cardiovascular risk |journal=British Medical Journal |date=Jan 24, 2018 |volume=360 |pages=k167 |doi=10.1136/bmj.k167|pmid=29367307 |s2cid=46825572 }}</ref><ref>{{cite journal |title=Just one cigarette a day can cause serious heart problems |journal=New Scientist |date=Feb 3, 2020 |url=https://www.newscientist.com/article/2159464-just-one-cigarette-a-day-can-cause-serious-heart-problems/}}</ref>

If someone stops smoking, then these chances gradually decrease as the damage to their body is repaired. A year after quitting, the risk of contracting heart disease is half that of a continuing smoker.<ref name="urlBenefits of Quitting - American Lung Association">{{cite web | url =http://www.lung.org/stop-smoking/how-to-quit/why-quit/benefits-of-quitting/ | title = Benefits of Quitting – American Lung Association | work = Stop Smoking | publisher = [[American Lung Association]] | access-date = 2012-05-06 }}</ref> The health risks of smoking are not uniform across all smokers. Risks vary according to the amount of tobacco smoked, with those who smoke more at greater risk. Smoking so-called "light" cigarettes does not reduce the risk.<ref>{{cite web|url=http://www.cancer.gov/cancertopics/factsheet/Tobacco/light-cigarettes|title=Light Cigarettes and Cancer Risk|work=National Cancer Institute|access-date=8 September 2014|date=2005-08-18}}</ref>

=== Mortality ===
Smoking is the cause of about 5 million deaths per year.<ref>{{cite journal | vauthors = Rizzuto D, Fratiglioni L | title = Lifestyle factors related to mortality and survival: a mini-review | journal = Gerontology | volume = 60 | issue = 4 | pages = 327–35 | date = 2014 | pmid = 24557026 | doi = 10.1159/000356771 | doi-access = free }}</ref> This makes it the most common cause of preventable early death.<ref>{{cite journal | vauthors = Samet JM | title = Tobacco smoking: the leading cause of preventable disease worldwide | journal = Thoracic Surgery Clinics | volume = 23 | issue = 2 | pages = 103–12 | date = May 2013 | pmid = 23566962 | doi = 10.1016/j.thorsurg.2013.01.009 }}</ref> One study found that male and female smokers lose an average of 13.2 and 14.5 years of life, respectively.<ref name="pmid12002168">{{cite journal | author = Centers for Disease Control and Prevention (CDC) | title = Annual smoking-attributable mortality, years of potential life lost, and economic costs—United States, 1995–1999 | journal = MMWR. Morbidity and Mortality Weekly Report | volume = 51 | issue = 14 | pages = 300–3 | date = April 2002 | pmid = 12002168 }}</ref> Another measured a loss of life of 6.8 years.<ref>{{cite journal | vauthors = Streppel MT, Boshuizen HC, Ocké MC, Kok FJ, Kromhout D | title = Mortality and life expectancy in relation to long-term cigarette, cigar and pipe smoking: the Zutphen Study | journal = Tobacco Control | volume = 16 | issue = 2 | pages = 107–13 | date = April 2007 | pmid = 17400948 | pmc = 2598467 | doi = 10.1136/tc.2006.017715 }}</ref> Each cigarette that is smoked is estimated to shorten life by an average of 11 minutes, though this may vary slightly on the contents and brand.<ref name=m11>{{cite web |url=http://www.nyc.gov/html/doh/downloads/pdf/chi/chi24-4-pktguide.pdf |title= Treating Nicotine Addiction | work = The New York City Department of Health and Mental Hygiene |access-date=2009-11-13 |url-status=dead |archive-url=https://web.archive.org/web/20091229042543/http://www.nyc.gov/html/doh/downloads/pdf/chi/chi24-4-pktguide.pdf |archive-date=2009-12-29 }}</ref><ref>{{cite news|url=http://news.bbc.co.uk/1/hi/health/583722.stm |title=HEALTH &#124; Cigarettes 'cut life by 11 minutes' |work=BBC News |date=1999-12-31 |access-date=2012-03-25}}</ref><ref>{{cite journal|title=Time for a smoke? One cigarette reduces your life by 11 minutes |journal=BMJ |volume=320 |issue=7226 |pages=53 |doi=10.1136/bmj.320.7226.53 |pmid=10617536 |pmc=1117323 |year=2000 | vauthors = Shaw M }}</ref> At least half of all lifelong smokers die early as a result of smoking.<ref name="Doll_2004"/> Smokers are three times more likely to die before the age of 60 or 70 than non-smokers.<ref name="Doll_2004"/><ref>{{cite journal | vauthors = Mamun AA, Peeters A, Barendregt J, Willekens F, Nusselder W, Bonneux L | title = Smoking decreases the duration of life lived with and without cardiovascular disease: a life course analysis of the Framingham Heart Study | journal = European Heart Journal | volume = 25 | issue = 5 | pages = 409–15 | date = March 2004 | pmid = 15033253 | doi = 10.1016/j.ehj.2003.12.015 | doi-access = free }}</ref><ref name="pmid7661229">{{cite journal | vauthors = Thun MJ, Day-Lally CA, Calle EE, Flanders WD, Heath CW | title = Excess mortality among cigarette smokers: changes in a 20-year interval | journal = American Journal of Public Health | volume = 85 | issue = 9 | pages = 1223–30 | date = September 1995 | pmid = 7661229 | pmc = 1615570 | doi = 10.2105/AJPH.85.9.1223 }}</ref>

In the United States, cigarette smoking and exposure to tobacco smoke accounts for roughly one in five,<ref name="urlwww.americashealthrankings.org">{{cite web | url =http://www.americashealthrankings.org/SiteFiles/Reports/AHR%202011Edition.pdf | title = America's Health Rankings – 2011 |date=December 2011  | publisher = United Health Foundation | pages = 12 }}</ref> or at least 443,000 premature deaths annually.<ref name="pmid19008791">{{cite journal | author = Centers for Disease Control and Prevention (CDC) | title = Smoking-attributable mortality, years of potential life lost, and productivity losses—United States, 2000–2004 | journal = MMWR. Morbidity and Mortality Weekly Report | volume = 57 | issue = 45 | pages = 1226–8 | date = November 2008 | pmid = 19008791 }}</ref> To put this into context, ABC's [[Peter Jennings]] (who would later die at 67 from complications of lung cancer caused by life-long smoking) famously reported that in the US alone, tobacco kills the equivalent of three [[Wide-body aircraft|jumbo jets]] full of people crashing every day, with no survivors.<ref>Never Say Die, an ABC News special by Peter Jennings 6/27/1996</ref> On a worldwide basis, this equates to a single jumbo jet every hour.<ref>{{cite journal | year = 2007 | title = 21st Century Could See a Billion Tobacco Victims | journal = Tobacco News Flash | volume = 3 | issue = 12 | pages = 1 | url = http://ws.missouristate.edu/breatheeasymo/upload/Newsletters/Newsletter62.pdf | access-date = 2012-05-06 | url-status = dead | archive-url = https://web.archive.org/web/20120426021638/https://ws.missouristate.edu/breatheeasymo/upload/Newsletters/Newsletter62.pdf | archive-date = 2012-04-26 }}</ref>

A 2015 study found that about 17% of mortality due to cigarette smoking in the United States is due to diseases other than those usually believed to be related.<ref name="NEJM-20150212">{{cite journal | vauthors = Carter BD, Abnet CC, Feskanich D, Freedman ND, Hartge P, Lewis CE, Ockene JK, [[Prentice RL]], Speizer FE, Thun MJ, Jacobs EJ | title = Smoking and mortality—beyond established causes | journal = The New England Journal of Medicine | volume = 372 | issue = 7 | pages = 631–40 | date = February 2015 | pmid = 25671255 | doi = 10.1056/NEJMsa1407211 | s2cid = 34821377 | url = https://semanticscholar.org/paper/44b89f62528e1aee83592be7853a19afaf6c5415 }}</ref>

It is estimated that there are between 1 and 1.4 deaths per million cigarettes smoked. In fact, cigarette factories are the most deadly factories in the history of the world.<ref name="Proctor 87–91">{{Cite journal| vauthors = Proctor RN |date=2012-02-16|title=The history of the discovery of the cigarette–lung cancer link: evidentiary traditions, corporate denial, global toll: Table 1|journal=Tobacco Control|volume=21|issue=2|pages=87–91|doi=10.1136/tobaccocontrol-2011-050338|pmid=22345227|issn=0964-4563|doi-access=free}}</ref><ref>{{Cite journal| vauthors = Cohen BL |date=September 1991|title=Catalog of Risks Extended and Updated|journal=Health Physics|volume=61|issue=3|pages=317–335|doi=10.1097/00004032-199109000-00002|pmid=1880022|issn=0017-9078}}</ref> See the below chart detailing the highest-producing cigarette factories, and their estimated deaths caused annually due to the health detriments of cigarettes.<ref name="Proctor 87–91"/>
<!-- Deleted image removed: [[File:Cigarette factory output.png|none|thumb|World's largest cigarette factories and their estimated deaths caused annually.]] -->

<gallery widths="360px" heights="240px">
File:Share-deaths-smoking.png|Share of deaths from smoking, 2017<ref>{{cite web |title=Share of deaths from smoking |url=https://ourworldindata.org/grapher/share-deaths-smoking |website=Our World in Data |access-date=5 March 2020}}</ref>
File:Death-rate-smoking.png|The number of deaths attributed to smoking per 100,000 people in 2017<ref>{{cite web |title=Death rate from smoking |url=https://ourworldindata.org/grapher/death-rate-smoking?tab=map |website=Our World in Data |access-date=5 March 2020}}</ref>
</gallery>

=== Cancer ===
[[File:Share-of-cancer-deaths-attributed-to-tobacco.png|thumb|upright=1.6|Share of cancer deaths attributed to tobacco in 2016<ref>{{cite web |title=Share of cancer deaths attributed to tobacco |url=https://ourworldindata.org/grapher/share-of-cancer-deaths-attributed-to-tobacco |website=Our World in Data |access-date=5 March 2020}}</ref>]]
[[File:What Smoking Does to Your Lungs - The Cold Hard Facts - The Real Cost.webm|thumb|right|Effects of smoking include both immediate and long-term lung damage.|alt=Effects of smoking include both immediate and long-term lung damage.]]
The primary risks of tobacco usage include many forms of cancer, particularly [[lung cancer]],<ref name="urlwww.legacyforhealth.org">{{cite web | url = http://www.legacyforhealth.org/PDFPublications/Lung_Cancer_and_Smoking.pdf | title = Lung Cancer and Smoking | date = 2010-11-23 | work = Fact Sheet | publisher = www.LegacyForHealth.org | access-date = 2012-05-06 | archive-url = https://web.archive.org/web/20130315104053/https://www.legacyforhealth.org/PDFPublications/Lung_Cancer_and_Smoking.pdf | archive-date = 2013-03-15 | url-status = dead }}</ref> [[kidney cancer]],<ref>{{cite journal | vauthors = Lipworth L, Tarone RE, McLaughlin JK | title = The epidemiology of renal cell carcinoma | journal = The Journal of Urology | volume = 176 | issue = 6 Pt 1 | pages = 2353–8 | date = December 2006 | pmid = 17085101 | doi = 10.1016/j.juro.2006.07.130 }}</ref> [[Laryngeal cancer|cancer of the larynx]] and [[Head and neck cancer|head and neck]],<ref>{{cite web | url=http://www.cancerresearchuk.org/about-cancer/type/larynx-cancer/about/risks-and-causes-of-laryngeal-cancer | title=Risks and causes of laryngeal cancer | work=Cancer Research UK | access-date=21 June 2015}}</ref><ref>{{cite web | url=http://www.cancer.net/cancer-types/head-and-neck-cancer/risk-factors-and-prevention | title=Head and Neck Cancer: Risk Factors and Prevention | publisher=ASCO | access-date=21 June 2015| date=2012-06-26 }}</ref> [[bladder cancer]],<ref>{{cite journal | vauthors = Boffetta P | title = Tobacco smoking and risk of bladder cancer | journal = Scandinavian Journal of Urology and Nephrology. Supplementum | volume = 42 | issue = 218 | pages = 45–54 | date = September 2008 | pmid = 18815916 | doi = 10.1080/03008880802283664 | s2cid = 39577281 }}</ref> [[esophageal cancer|cancer of the esophagus]],<ref name="url_www.cancer.org_EsophagusCancer">{{cite web | url =http://www.cancer.org/Cancer/EsophagusCancer/DetailedGuide/esophagus-cancer-risk-factors | title = Esophagus Cancer | date = 2011-08-11  | publisher = American Cancer Society | access-date = 2012-05-06 }}</ref> [[pancreatic cancer|cancer of the pancreas]]<ref>{{cite journal | vauthors = Iodice S, Gandini S, Maisonneuve P, Lowenfels AB | title = Tobacco and the risk of pancreatic cancer: a review and meta-analysis | journal = Langenbeck's Archives of Surgery | volume = 393 | issue = 4 | pages = 535–45 | date = July 2008 | pmid = 18193270 | doi = 10.1007/s00423-007-0266-2 | s2cid = 23516238 }}</ref> and [[stomach cancer]].<ref name=jinternmed>{{cite journal | vauthors = Kuper H, Boffetta P, Adami HO | title = Tobacco use and cancer causation: association by tumour type | journal = Journal of Internal Medicine | volume = 252 | issue = 3 | pages = 206–24 | date = September 2002 | pmid = 12270001 | doi = 10.1046/j.1365-2796.2002.01022.x | s2cid = 6132726 | url = https://semanticscholar.org/paper/61b7b567fcdfcc53dd4618538947d383d7a8e5f0 }}</ref> Studies have established a firm relationship between tobacco smoke, including second-hand smoke, and [[cervical cancer]] in women.<ref>{{cite journal | vauthors = Vineis P, Alavanja M, Buffler P, Fontham E, Franceschi S, Gao YT, Gupta PC, Hackshaw A, Matos E, Samet J, Sitas F, Smith J, Stayner L, Straif K, Thun MJ, Wichmann HE, Wu AH, Zaridze D, Peto R, Doll R | title = Tobacco and cancer: recent epidemiological evidence | journal = Journal of the National Cancer Institute | volume = 96 | issue = 2 | pages = 99–106 | date = January 2004 | pmid = 14734699 | doi = 10.1093/jnci/djh014 | doi-access = free }}</ref> There is some evidence suggesting a small increased risk of [[myeloid leukemia]],<ref>{{cite journal | vauthors = Sasco AJ, Secretan MB, Straif K | title = Tobacco smoking and cancer: a brief review of recent epidemiological evidence | journal = Lung Cancer | volume = 45 | issue = Suppl 2 | pages = S3–9 | date = August 2004 | pmid = 15552776 | doi = 10.1016/j.lungcan.2004.07.998 }}</ref> [[Squamous cell carcinoma|squamous cell sinonasal cancer]], [[liver cancer]], [[colorectal cancer]], cancers of [[Gallbladder cancer|the gallbladder]], [[Adrenocortical carcinoma|the adrenal gland]], [[Small intestine cancer|the small intestine]], and various childhood cancers.<ref name=jinternmed/> The possible connection between [[breast cancer]] and tobacco is still uncertain.<ref>{{cite web | url=http://www.cancer.org/cancer/breastcancer/detailedguide/breast-cancer-risk-factors | title=What are the risk factors for breast cancer? | work=American Cancer Society | access-date=31 May 2015}}</ref>{{medical citation needed|date=March 2017}}

The risk of lung cancer risk is highly influenced by smoking, with up to 90% of diagnoses being attributed to tobacco smoking.<ref>Pesch, B., Kendzia, B., Gustavsson, P., Jöckel, K.-H., Johnen, G., Pohlabeln, H., … Brüning, T. (2012). Cigarette smoking and lung cancer – relative risk estimates for the major histological types from a pooled analysis of case-control studies. International Journal of Cancer. Journal International Du Cancer, 131(5), 1210–1219.</ref> The risk of developing lung cancer increases with the number of years smoking and number of cigarettes smoked per day.<ref>{{cite web | publisher = United States Department of Health & Human Services. | title = Reducing the Health Consequences of Smoking: 25 Years of Progress. A Report of the Surgeon General. | url = http://profiles.nlm.nih.gov/ps/retrieve/ResourceMetadata/NNBBXS | access-date = 1 November 2012 }}</ref> Smoking can be linked to all subtypes of lung cancer. [[Small-cell carcinoma]] (SCLC) is the most closely associated with almost 100% of cases occurring in smokers.<ref>{{cite journal | vauthors = Kalemkerian GP, Akerley W, Rogner P, Borghaei H, Chow L, Downey RJ, Gandhi L, Ganti AK, Govindan R, Grecula JC, Hayman J | display-authors = 6 | title = Small cell lung cancer clinical practice guidelines in oncology. | journal = Journal of the National Comprehensive Cancer Network | date = October 2011 | volume = 9 | issue = 10 | pages = 1086–113  | doi = 10.6004/jnccn.2011.0092 | pmid = 21975911 }}</ref> This form of cancer has been identified with autocrine growth loops, [[proto-oncogene]] activation and inhibition of [[Tumor suppressor gene|tumour suppressor genes]]. SCLC may originate from neuroendocrine cells located in the bronchus called Feyrter cells.<ref>{{cite journal | vauthors = Champaneria MC, Modlin IM, Kidd M, Eick GN | title = Friedrich Feyrter: a precise intellect in a diffuse system | journal = Neuroendocrinology | volume = 83 | issue = 5–6 | pages = 394–404 | year = 2006 | pmid = 17028417 | doi = 10.1159/000096050 | s2cid = 25627846 }}</ref>

The risk of dying from lung cancer before age 85 is 22.1% for a male smoker and 11.9% for a female smoker, in the absence of competing causes of death. The corresponding estimates for lifelong nonsmokers are a 1.1% probability of dying from lung cancer before age 85 for a man of European descent, and a 0.8% probability for a woman.<ref>{{cite journal | vauthors = Thun MJ, Hannan LM, Adams-Campbell LL, Boffetta P, Buring JE, Feskanich D, Flanders WD, Jee SH, Katanoda K, Kolonel LN, Lee IM, Marugame T, Palmer JR, Riboli E, Sobue T, Avila-Tang E, Wilkens LR, Samet JM | title = Lung cancer occurrence in never-smokers: an analysis of 13 cohorts and 22 cancer registry studies | journal = PLOS Medicine | volume = 5 | issue = 9 | pages = e185 | date = September 2008 | pmid = 18788891 | pmc = 2531137 | doi = 10.1371/journal.pmed.0050185 }}</ref>

=== Pulmonary ===
[[File:Cancer smoking lung cancer correlation from NIH.svg|thumb|Since establishing causation through experimental trials was not possible due to ethical restrictions, a lengthy study was conducted in order to establish the strong association necessary to allow for legislative action against tobacco consumption.{{Citation needed|date=May 2009}}]]

In smoking, long term exposure to compounds found in the smoke (e.g., [[carbon monoxide]] and [[cyanide]]) are believed to be responsible for pulmonary damage and for loss of elasticity in the [[pulmonary alveolus|alveoli]], leading to emphysema and [[chronic obstructive pulmonary disease]] (COPD).<ref name="IJERPH 2009">{{cite journal | vauthors = Laniado-Laborín R |date=January 2009 |title=Smoking and Chronic Obstructive Pulmonary Disease (COPD). Parallel Epidemics of the 21st Century |journal=[[International Journal of Environmental Research and Public Health]] |publisher=[[MDPI]] |volume=6 |issue=1: ''Smoking and Tobacco Control'' |doi=10.3390/ijerph6010209 |pages=209–224 |doi-access=free |issn=1660-4601 |pmc=2672326 |pmid=19440278 |s2cid=19615031 }}</ref> COPD caused by smoking is a permanent, incurable (often terminal) reduction of pulmonary capacity characterised by shortness of breath, wheezing, persistent cough with [[sputum]], and damage to the lungs, including [[emphysema]] and [[Bronchitis#Chronic bronchitis|chronic bronchitis]].<ref>{{cite journal | vauthors = Devereux G | title = ABC of chronic obstructive pulmonary disease. Definition, epidemiology, and risk factors | journal = BMJ | volume = 332 | issue = 7550 | pages = 1142–4 | date = May 2006 | pmid = 16690673 | pmc = 1459603 | doi = 10.1136/bmj.332.7550.1142 }}</ref> The carcinogen acrolein and its derivatives also contribute to the chronic inflammation present in COPD.<ref name="Facchinetti">{{cite journal | vauthors = Facchinetti F, Amadei F, Geppetti P, Tarantini F, Di Serio C, Dragotto A, Gigli PM, Catinella S, Civelli M, Patacchini R | title = Alpha,beta-unsaturated aldehydes in cigarette smoke release inflammatory mediators from human macrophages | journal = American Journal of Respiratory Cell and Molecular Biology | volume = 37 | issue = 5 | pages = 617–23 | date = November 2007 | pmid = 17600310 | doi = 10.1165/rcmb.2007-0130OC }}</ref>

=== Cardiovascular disease ===
[[File:Smoking and Atherosclerosis.jpg|thumb|Smoking can cause [[atherosclerosis]], leading to [[coronary artery disease]] and [[peripheral arterial disease]].]]

[[File:Nicotine stains10.JPG|thumb|Tobacco stains on primarily the second and third fingers of a heavy smoker]]

Inhalation of tobacco smoke causes several immediate responses within the heart and blood vessels. Within one minute the heart rate begins to rise, increasing by as much as 30 percent during the first 10 minutes of smoking. Carbon monoxide in tobacco smoke exerts [[carbon monoxide poisoning|negative effects]] by reducing the blood's ability to carry oxygen.<ref>{{cite journal | vauthors = Glantz SA, Parmley WW | title = Passive smoking and heart disease. Mechanisms and risk | journal = JAMA | volume = 273 | issue = 13 | pages = 1047–53 | date = April 1995 | pmid = 7897790 | doi = 10.1001/jama.1995.03520370089043 | citeseerx = 10.1.1.598.9772 }}</ref>

Smoking also increases the chance of [[heart disease]], [[stroke]], [[atherosclerosis]], and [[peripheral vascular disease]].<ref>{{cite journal | vauthors = Shah RS, Cole JW | title = Smoking and stroke: the more you smoke the more you stroke | journal = Expert Review of Cardiovascular Therapy | volume = 8 | issue = 7 | pages = 917–32 | date = July 2010 | pmid = 20602553 | pmc = 2928253 | doi = 10.1586/erc.10.56 }}</ref><ref>{{cite web | url=http://www.nhlbi.nih.gov/health/health-topics/topics/smo | title=How Does Smoking Affect the Heart and Blood Vessels? | publisher=NHLBI | access-date=9 September 2015}}</ref> Several ingredients of tobacco lead to the narrowing of blood vessels, increasing the likelihood of a blockage, and thus a [[myocardial infarction|heart attack]] or stroke. According to a study by an international team of researchers, people under 40 are five times more likely to have a heart attack if they are smokers.<ref name="news.bbc.co.uk.330">{{Cite news|title=Health : Young smokers' heart attack risk|url=http://news.bbc.co.uk/2/hi/health/3590320.stm|access-date=2005-12-18|publisher=BBC  | date=2004-08-24}}</ref><ref name="pmid15333879">{{cite journal | vauthors=Mähönen MS, McElduff P, Dobson AJ, Kuulasmaa KA, Evans AE | title=Current smoking and the risk of non-fatal myocardial infarction in the WHO MONICA Project populations | journal= [[Tobacco Control (journal)|Tobacco Control]] | volume=13 |issue=3 | pages=244–250 | year=2004 | doi=10.1136/tc.2003.003269 | pmc=1747894 | pmid = 15333879 }}</ref>

Exposure to tobacco smoke is known to increase oxidative stress in the body by various mechanisms, including depletion of plasma antioxidants such as [[vitamin C]].<ref>{{cite journal | vauthors = Saha SP, Bhalla DK, Whayne TF, Gairola C | title = Cigarette smoke and adverse health effects: An overview of research trends and future needs | journal = The International Journal of Angiology | volume = 16 | issue = 3 | pages = 77–83 | date = Autumn 2007 | pmid = 22477297 | pmc = 2733016 | doi = 10.1055/s-0031-1278254 }}</ref>

Research by American biologists has shown that cigarette smoke also influences the process of cell division in the cardiac muscle and changes the heart's shape.<ref name="InfoNIAC.com">{{Cite news|title=Cigarette Smoke Changes Heart's Shape|url=http://www.infoniac.com/health-fitness/cigarette-smoke-changes-heart-s-shape.html|access-date=2009-01-10|publisher=InfoNIAC.com}}</ref>

The usage of tobacco has also been linked to [[Buerger's disease]] (''thromboangiitis obliterans''), the acute inflammation and thrombosis (clotting) of arteries and veins of the hands and feet.<ref>{{cite journal | vauthors = Joyce JW | title = Buerger's disease (thromboangiitis obliterans) | journal = Rheumatic Disease Clinics of North America | volume = 16 | issue = 2 | pages = 463–70 | date = May 1990 | doi = 10.1016/S0889-857X(21)01071-1 | pmid = 2189162 }}</ref>

Although cigarette smoking causes a greater increase in the risk of cancer than cigar smoking, cigar smokers still have an increased risk for many health problems, including cancer, when compared to non-smokers.<ref name="Burns"/><ref name="Symm_2005">{{cite journal | vauthors = Symm B, Morgan MV, Blackshear Y, Tinsley S | title = Cigar smoking: an ignored public health threat | journal = The Journal of Primary Prevention | volume = 26 | issue = 4 | pages = 363–75 | date = July 2005 | pmid = 15995804 | doi = 10.1007/s10935-005-5389-z | s2cid = 23999589 | department = Secdondary }}</ref> As for second-hand smoke, the NIH study points to the large amount of smoke generated by one cigar, saying "cigars can contribute substantial amounts of tobacco smoke to the indoor environment; and, when large numbers of cigar smokers congregate in a cigar smoking event, the amount of ETS (i.e. second-hand smoke) produced is sufficient to be a health concern for those regularly required to work in those environments."<ref name=NIH/>

Smoking also tends to [[Hypercholesterolemia|increase blood cholesterol levels]]. Furthermore, the ratio of [[high-density lipoprotein]] (HDL, also known as the "good" cholesterol) to [[low-density lipoprotein]] (LDL, also known as the "bad" cholesterol) tends to be lower in smokers compared to non-smokers. Smoking also raises the levels of [[fibrinogen]] and increases [[platelet]] production (both involved in blood clotting) which makes the blood thicker and more likely to clot. Carbon monoxide binds to [[hemoglobin]] (the oxygen-carrying component in red blood cells), resulting in a much stabler complex than hemoglobin bound with oxygen or carbon dioxide—the result is permanent loss of blood cell functionality. Blood cells are naturally recycled after a certain period of time, allowing for the creation of new, functional red blood cells. However, if carbon monoxide exposure reaches a certain point before they can be recycled, hypoxia (and later death) occurs. All these factors make smokers more at risk of developing various forms of [[arteriosclerosis]] (hardening of the arteries). As the arteriosclerosis progresses, blood flows less easily through rigid and narrowed blood vessels, making the blood more likely to form a thrombosis (clot). Sudden blockage of a blood vessel may lead to an infarction (stroke or heart attack). However, it is also worth noting that the effects of smoking on the heart may be more subtle. These conditions may develop gradually given the smoking-healing cycle (the human body heals itself between periods of smoking), and therefore a smoker may develop less significant disorders such as worsening or maintenance of unpleasant dermatological conditions, e.g. eczema, due to reduced blood supply. Smoking also increases [[blood pressure]] and weakens blood vessels.<ref name="Narkiewicz_2005"/>

=== Renal ===
In addition to increasing the risk of kidney cancer, smoking can also contribute to additional [[renal]] damage. Smokers are at a significantly increased risk for [[chronic kidney disease]] than non-smokers.<ref name="pmid21108832">{{cite journal | vauthors = Yacoub R, Habib H, Lahdo A, Al Ali R, Varjabedian L, Atalla G, Kassis Akl N, Aldakheel S, Alahdab S, Albitar S | title = Association between smoking and chronic kidney disease: a case control study | journal = BMC Public Health | volume = 10 | pages = 731 | date = November 2010 | pmid = 21108832 | pmc = 3004836 | doi = 10.1186/1471-2458-10-731 }}</ref> A history of smoking encourages the progression of [[diabetic nephropathy]].<ref name="pmid8137682">{{cite journal | vauthors = Sawicki PT, Didjurgeit U, Mühlhauser I, Bender R, Heinemann L, Berger M | title = Smoking is associated with progression of diabetic nephropathy | journal = Diabetes Care | volume = 17 | issue = 2 | pages = 126–31 | date = February 1994 | pmid = 8137682 | doi = 10.2337/diacare.17.2.126 | s2cid = 22581830 }}</ref>

=== Influenza ===
A study of an outbreak of an ([[Influenza A virus subtype H1N1|H1N1]]) influenza in an Israeli military unit of 336 healthy young men to determine the relation of cigarette smoking to the incidence of clinically apparent influenza, revealed that, of 168 smokers, 68.5 percent had influenza, as compared with 47.2 percent of nonsmokers. Influenza was also more severe in the smokers; 50.6 percent of them lost work days or required bed rest, or both, as compared with 30.1 percent of the nonsmokers.<ref name="Kark_1982">{{cite journal | vauthors = Kark JD, Lebiush M, Rannon L | title = Cigarette smoking as a risk factor for epidemic a(h1n1) influenza in young men | journal = The New England Journal of Medicine | volume = 307 | issue = 17 | pages = 1042–6 | date = October 1982 | pmid = 7121513 | doi = 10.1056/NEJM198210213071702 }}</ref>

According to a study of 1,900 male cadets after the 1968 Hong Kong A2 influenza epidemic at a South Carolina military academy, compared with nonsmokers, heavy smokers (more than 20 cigarettes per day) had 21% more illnesses and 20% more bed rest, light smokers (20 cigarettes or fewer per day) had 10% more illnesses and 7% more bed rest.<ref name="Finklea_1969">{{cite journal | vauthors = Finklea JF, Sandifer SH, Smith DD | title = Cigarette smoking and epidemic influenza | journal = American Journal of Epidemiology | volume = 90 | issue = 5 | pages = 390–9 | date = November 1969 | pmid = 5356947 | doi = 10.1093/oxfordjournals.aje.a121084 }}</ref>

The effect of cigarette smoking upon epidemic influenza was studied prospectively among 1,811 male college students. Clinical influenza incidence among those who daily smoked 21 or more cigarettes was 21% higher than that of non-smokers. Influenza incidence among smokers of 1 to 20 cigarettes daily was intermediate between non-smokers and heavy cigarette smokers.<ref name="Finklea_1969"/>

Surveillance of a 1979 influenza outbreak at a military base for women in Israel revealed that influenza symptoms developed in 60.0% of the current smokers vs. 41.6% of the nonsmokers.<ref name="pmid7212144">{{cite journal | vauthors = Kark JD, Lebiush M | title = Smoking and epidemic influenza-like illness in female military recruits: a brief survey | journal = American Journal of Public Health | volume = 71 | issue = 5 | pages = 530–2 | date = May 1981 | pmid = 7212144 | pmc = 1619723 | doi = 10.2105/AJPH.71.5.530 }}</ref>

Smoking seems to cause a higher relative influenza-risk in older populations than in younger populations. In a prospective study of community-dwelling people 60–90 years of age, during 1993, of unimmunized people 23% of smokers had clinical influenza as compared with 6% of non-smokers.<ref name="pmid10487646">{{cite journal | vauthors = Nicholson KG, Kent J, Hammersley V | title = Influenza A among community-dwelling elderly persons in Leicestershire during winter 1993-4; cigarette smoking as a risk factor and the efficacy of influenza vaccination | journal = Epidemiology and Infection | volume = 123 | issue = 1 | pages = 103–8 | date = August 1999 | pmid = 10487646 | pmc = 2810733 | doi = 10.1017/S095026889900271X }}</ref>

Smoking may substantially contribute to the growth of influenza epidemics affecting the entire population.<ref name="Kark_1982"/> However, the proportion of influenza cases in the general non-smoking population attributable to smokers has not yet been calculated.{{citation needed|date=October 2016}}

=== Mouth ===
[[File:Bone loss in periapical xray.jpg|thumb|Dental radiograph showing bone loss in a 32 year old heavy smoker]]
Perhaps the most serious oral condition that can arise is that of [[oral cancer]]. However, smoking also increases the risk for various other oral diseases, some almost completely exclusive to tobacco users. The [[National Institutes of Health]], through the [[National Cancer Institute]], determined in 1998 that "cigar smoking causes a variety of cancers including cancers of the [[oral cancer|oral cavity]] (lip, tongue, mouth, throat), [[Esophageal cancer|esophagus]], [[Laryngeal cancer|larynx]], and [[lung cancer|lung]]."<ref name=NIH>{{cite web|url=http://www.nih.gov/news/pr/apr98/nci-10a.htm|title=Background on Cigar Monograph: Cigars: Health Effects and Trends|date=1998-04-10|access-date=2008-01-04|author=National Institutes of Health|url-status=dead|archive-url=https://web.archive.org/web/20080513163941/http://www.nih.gov/news/pr/apr98/nci-10a.htm|archive-date=2008-05-13|author-link=National Institutes of Health}}</ref> [[Smoking pipe (tobacco)|Pipe]] smoking involves significant health risks,<ref>{{cite journal|title=Questions About Smoking, Tobacco, and Health|journal=Journal of the National Cancer Institute|volume=96|issue=11|pages=853–861|author=American Cancer Society|doi=10.1093/jnci/djh144|pmid=15173269|year=2004|author-link=American Cancer Society|doi-access=free}}</ref><ref>{{cite journal | vauthors = Henley SJ, Thun MJ, Chao A, Calle EE | title = Association between exclusive pipe smoking and mortality from cancer and other diseases | journal = Journal of the National Cancer Institute | volume = 96 | issue = 11 | pages = 853–61 | date = June 2004 | pmid = 15173269 | doi = 10.1093/jnci/djh144 | doi-access = free }}</ref> particularly oral cancer.<ref>{{cite book|url=http://books.nap.edu/openbook.php?record_id=943&page=250|author=Commission on Life Sciences|title=Environmental Tobacco Smoke: Measuring Exposures and Assessing Health Effects (1986)|year=1986|doi=10.17226/943|pmid=25032469|isbn=978-0-309-03730-3|access-date=2008-01-04}}</ref> Roughly half of [[periodontitis]] or inflammation around the teeth cases are attributed to current or former smoking. Smokeless tobacco causes [[Receding gums|gingival recession]] and white mucosal [[lesion]]s. Up to 90% of periodontitis patients who are not helped by common modes of treatment are smokers. Smokers have significantly greater loss of bone height than nonsmokers, and the trend can be extended to pipe smokers to have more bone loss than nonsmokers.<ref name="pmid11336116">{{cite journal | vauthors = Johnson GK, Slach NA | title = Impact of tobacco use on periodontal status | journal = Journal of Dental Education | volume = 65 | issue = 4 | pages = 313–21 | date = April 2001 | doi = 10.1002/j.0022-0337.2001.65.4.tb03401.x | pmid = 11336116 }}</ref>

Smoking has been proven to be an important factor in the staining of teeth.<ref name="pmid12707498">{{cite journal | vauthors = Reibel J | title = Tobacco and oral diseases. Update on the evidence, with recommendations | journal = Medical Principles and Practice | volume = 12 | issue = Suppl 1 | pages = 22–32 | year = 2003 | pmid = 12707498 | doi = 10.1159/000069845 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Ness L, Rosekrans D, Welford JF | title = An epidemiologic study of factors affecting extrinsic staining of teeth in an English population | journal = Community Dentistry and Oral Epidemiology | volume = 5 | issue = 1 | pages = 55–60 | date = January 1977 | pmid = 264419 | doi = 10.1111/j.1600-0528.1977.tb01617.x }}</ref> [[Halitosis]] or bad breath is common among tobacco smokers.<ref>{{cite web|url=http://www.iwant2stopsmoking.com|title=Helping you to Stop Smoking!|access-date=2008-01-04|archive-url=https://web.archive.org/web/20080828131627/http://www.iwant2stopsmoking.com/|archive-date=2008-08-28|url-status=dead}}</ref> Tooth loss has been shown to be 2<ref>{{cite journal | vauthors = Züllich G, Damm KH, Braun W, Lisboa BP | title = Studies on biliary excreted metabolites of [G-3H]digitoxin in rats | journal = Archives Internationales de Pharmacodynamie et de Therapie | volume = 215 | issue = 1 | pages = 160–7 | date = May 1975 | pmid = 1156044 }}</ref> to 3 times<ref>{{cite journal | vauthors = Dietrich T, Maserejian NN, Joshipura KJ, Krall EA, Garcia RI | title = Tobacco use and incidence of tooth loss among US male health professionals | journal = Journal of Dental Research | volume = 86 | issue = 4 | pages = 373–7 | date = April 2007 | pmid = 17384035 | pmc = 2582143 | doi = 10.1177/154405910708600414 }}</ref> higher in smokers than in non-smokers.<ref>{{cite journal | vauthors = Al-Bayaty FH, Wahid NA, Bulgiba AM | title = Tooth mortality in smokers and nonsmokers in a selected population in Sana'a, Yemen | journal = Journal of Periodontal Research | volume = 43 | issue = 1 | pages = 9–13 | date = February 2008 | pmid = 18230101 | doi = 10.1111/j.1600-0765.2007.00988.x }}</ref> In addition, complications may further include [[leukoplakia]], the adherent white plaques or patches on the mucous membranes of the oral cavity, including the tongue.<ref>{{cite web | url=http://www.mayoclinic.org/diseases-conditions/leukoplakia/basics/causes/con-20023802 | title=Leukoplakia Causes | work=Mayo Clinic | access-date=31 May 2015}}</ref>

=== Infection ===
Smoking is also linked to susceptibility to infectious diseases, particularly in the lungs ([[pneumonia]]). Smoking more than 20 [[cigarette]]s a day increases the risk of tuberculosis by two to four times,<ref>{{cite journal | vauthors = Davies PD, Yew WW, Ganguly D, Davidow AL, Reichman LB, Dheda K, Rook GA | title = Smoking and tuberculosis: the epidemiological association and immunopathogenesis | journal = Transactions of the Royal Society of Tropical Medicine and Hygiene | volume = 100 | issue = 4 | pages = 291–8 | date = April 2006 | pmid = 16325875 | doi = 10.1016/j.trstmh.2005.06.034 }}</ref><ref>{{cite journal | vauthors = Jha P, Jacob B, Gajalakshmi V, Gupta PC, Dhingra N, Kumar R, Sinha DN, Dikshit RP, Parida DK, Kamadod R, Boreham J, Peto R | title = A nationally representative case-control study of smoking and death in India | journal = The New England Journal of Medicine | volume = 358 | issue = 11 | pages = 1137–47 | date = March 2008 | pmid = 18272886 | doi = 10.1056/NEJMsa0707719 | s2cid = 92980 | url = https://semanticscholar.org/paper/53e7989c3787c1a4bf8fb77f7a43e1b13f83b4e3 }}</ref> and being a current smoker has been linked to a fourfold increase in the risk of invasive disease caused by the pathogenic bacteria ''[[Streptococcus pneumoniae]]''.<ref>{{cite journal | vauthors = Nuorti JP, Butler JC, Farley MM, Harrison LH, McGeer A, Kolczak MS, Breiman RF | title = Cigarette smoking and invasive pneumococcal disease. Active Bacterial Core Surveillance Team | journal = The New England Journal of Medicine | volume = 342 | issue = 10 | pages = 681–9 | date = March 2000 | pmid = 10706897 | doi = 10.1056/NEJM200003093421002 }}</ref> It is believed that smoking increases the risk of these and other pulmonary and respiratory tract infections both through structural damage and through effects on the immune system. The effects on the immune system include an increase in CD4+ cell production attributable to nicotine, which has tentatively been linked to increased HIV susceptibility.<ref>{{cite journal | vauthors = Arcavi L, Benowitz NL | title = Cigarette smoking and infection | journal = Archives of Internal Medicine | volume = 164 | issue = 20 | pages = 2206–16 | date = November 2004 | pmid = 15534156 | doi = 10.1001/archinte.164.20.2206 | doi-access = free }}</ref>

Smoking increases the risk of [[Kaposi's sarcoma]] in people without [[HIV|HIV infection]].<ref>{{cite journal | vauthors = Goedert JJ, Vitale F, Lauria C, Serraino D, Tamburini M, Montella M, Messina A, Brown EE, Rezza G, Gafà L, Romano N | title = Risk factors for classical Kaposi's sarcoma | journal = Journal of the National Cancer Institute | volume = 94 | issue = 22 | pages = 1712–8 | date = November 2002 | pmid = 12441327 | doi = 10.1093/jnci/94.22.1712 | doi-access = free }}</ref> One study found this only with the male population and could not draw any conclusions for the female participants in the study.<ref>{{cite web|url=http://www.data-yard.net/10b/kaposi.htm|title=MEDLINEplus: Smoking Cuts Risk of Rare Cancer|access-date=8 September 2014}}</ref>

=== Impotence ===
The incidence of [[impotence]] (difficulty achieving and maintaining penile erection) is approximately 85 percent higher in male smokers compared to non-smokers.<ref name="tobaccoprogram.org">{{cite web|title=The Tobacco Reference Guide|url=http://www.tobaccoprogram.org/tobaccorefguide/ch12/ch12p1.htm|access-date=2006-07-15|url-status=dead|archive-url=https://web.archive.org/web/20060715183626/http://www.tobaccoprogram.org/tobaccorefguide/ch12/ch12p1.htm|archive-date=2006-07-15}}</ref> Smoking is a key cause of erectile dysfunction (ED).<ref name="pmid15924009">{{cite journal | vauthors = Peate I | title = The effects of smoking on the reproductive health of men | journal = British Journal of Nursing | volume = 14 | issue = 7 | pages = 362–6 | year = 2005 | pmid = 15924009 | doi = 10.12968/bjon.2005.14.7.17939 }}</ref><ref name="tobaccoprogram.org"/> It causes impotence because it promotes [[atherosclerosis|arterial narrowing]] and damages [[endothelial cell|cells lining the inside of the arteries]], thus leading to reduce penile blood flow.<ref name="pmid15753970">{{cite journal | vauthors = Kendirci M, Nowfar S, Hellstrom WJ | title = The impact of vascular risk factors on erectile function | journal = Drugs of Today | volume = 41 | issue = 1 | pages = 65–74 | date = January 2005 | pmid = 15753970 | doi = 10.1358/dot.2005.41.1.875779 }}</ref>

=== Female infertility ===
{{See also|Female infertility#Tobacco smoking}}

Smoking is harmful to the [[ovaries]], potentially causing [[female infertility]], and the degree of damage is dependent upon the amount and length of time a woman smokes. Nicotine and other harmful chemicals in cigarettes interfere with the body's ability to create [[estrogen]], a [[hormone]] that regulates [[folliculogenesis]] and [[ovulation]]. Also, cigarette smoking interferes with folliculogenesis, embryo transport, [[Endometrium|endometrial]] receptivity, endometrial [[angiogenesis]], uterine blood flow and the [[Uterus|uterine]] [[myometrium]].<ref>{{cite journal | vauthors = Dechanet C, Anahory T, Mathieu Daude JC, Quantin X, Reyftmann L, Hamamah S, Hedon B, Dechaud H | title = Effects of cigarette smoking on reproduction | journal = Human Reproduction Update | volume = 17 | issue = 1 | pages = 76–95 | year = 2011 | pmid = 20685716 | doi = 10.1093/humupd/dmq033 | doi-access = free }}</ref> Some damage is irreversible, but stopping smoking can prevent further damage.<ref name="asrm-risks">[http://www.protectyourfertility.com/femalerisks.html FERTILITY FACT > Female Risks] {{webarchive|url=https://web.archive.org/web/20070922184324/http://www.protectyourfertility.com/femalerisks.html |date=2007-09-22 }} By the American Society for Reproductive Medicine (ASRM). Retrieved on Jan 4, 2009</ref><ref>{{cite web|url=http://www.protectyourfertility.com/pdfs/magazine1_v4.pdf|title=protectyourfertility.com|access-date=8 September 2014|url-status=dead|archive-url=https://web.archive.org/web/20150924082509/http://www.protectyourfertility.com/pdfs/magazine1_v4.pdf|archive-date=24 September 2015}}</ref> Smokers are 60% more likely to be infertile than non-smokers.<ref name=dh2009/> Smoking reduces the chances of [[In vitro fertilisation|in vitro fertilization]] (IVF) producing a live birth by 34% and increases the risk of an IVF pregnancy miscarrying by 30%.<ref name=dh2009>[http://www.dh.gov.uk/en/Publicationsandstatistics/Publications/PublicationsPolicyAndGuidance/DH_101070Regulated fertility services: a commissioning aid – June 2009], from the Department of Health UK</ref>

=== Psychological ===
''[[American Psychologist]]'' stated, "Smokers often report that cigarettes help relieve feelings of stress. However, the stress levels of adult smokers are slightly higher than those of nonsmokers, adolescent smokers report increasing levels of stress as they develop regular patterns of smoking, and smoking cessation leads to reduced stress. Far from acting as an aid for mood control, nicotine dependency seems to exacerbate stress. This is confirmed in the daily mood patterns described by smokers, with normal moods during smoking and worsening moods between cigarettes. Thus, the apparent relaxant effect of smoking only reflects the reversal of the tension and irritability that develop during [[nicotine withdrawal|nicotine depletion]]. Dependent smokers need nicotine to remain feeling normal."<ref>{{cite journal | vauthors = Parrott AC | title = Does cigarette smoking cause stress? | journal = The American Psychologist | volume = 54 | issue = 10 | pages = 817–20 | date = October 1999 | pmid = 10540594 | doi = 10.1037/0003-066X.54.10.817 }}</ref>

==== Immediate effects ====
Users report feelings of [[Relaxation (psychology)|relaxation]], sharpness, [[calmness]], and [[alertness]].<ref name = "Lagrue_2001">{{cite journal |vauthors=Lagrue G, Lebargy F, Cormier A | year = 2001 | title = Des récepteurs nicotiniques à la dépendance tabagique : perspectives thérapeutiques |trans-title=From nicotinic receptors to smoking dependence: Therapeutic prospects | language = fr | journal = Alcoologie et Addictologie | volume = 23 | issue = 2 Suppl | pages = 39S–42S | url = http://bdoc.ofdt.fr/pmb/opac_css/index.php?lvl=notice_display&id=25200}}</ref> Those new to smoking may experience [[nausea]], [[dizziness]], increased blood pressure, narrowed arteries, and [[tachycardia|rapid heart beat]]. Generally, the unpleasant symptoms will eventually vanish over time, with repeated use, as the body builds a [[drug tolerance|tolerance]] to the chemicals in the cigarettes, such as [[nicotine]].{{citation needed|date=October 2016}}

==== Stress ====
Smokers report higher levels of everyday stress.<ref name="Addiction 1998">{{cite journal | vauthors = Parrott AC | title = Nesbitt's Paradox resolved? Stress and arousal modulation during cigarette smoking | journal = Addiction | volume = 93 | issue = 1 | pages = 27–39 | date = January 1998 | pmid = 9624709 | doi = 10.1046/j.1360-0443.1998.931274.x | citeseerx = 10.1.1.465.2496 }}</ref> Several studies have monitored feelings of stress over time and found reduced stress after quitting.<ref name="pmid1401384">{{cite journal | vauthors = Hughes JR | title = Tobacco withdrawal in self-quitters | journal = Journal of Consulting and Clinical Psychology | volume = 60 | issue = 5 | pages = 689–97 | date = October 1992 | pmid = 1401384 | doi = 10.1037/0022-006X.60.5.689 }}</ref><ref name="pmid2373070">{{cite journal | vauthors = Cohen S, Lichtenstein E | title = Perceived stress, quitting smoking, and smoking relapse | journal = Health Psychology | volume = 9 | issue = 4 | pages = 466–78 | year = 1990 | pmid = 2373070 | doi = 10.1037/0278-6133.9.4.466 | url = http://repository.cmu.edu/psychology/288 }}</ref>

The deleterious mood effects of everyday between-cigarette nicotine withdrawal symptoms explain why people who smoke experience more daily stress than non-smokers, and become less stressed when they quit smoking. Deprivation reversal also explains much of the arousal data, with deprived smokers being less vigilant and less alert than non-deprived smokers or non-smokers.<ref name="Addiction 1998"/>

Recent studies have shown a positive relationship between psychological distress and salivary [[cotinine]] levels in smoking and non-smoking adults, indicating that both firsthand and second-hand smoke exposure may lead to higher levels of mental stress.<ref name="pmid20529994">{{cite journal | vauthors = Hamer M, Stamatakis E, Batty GD | title = Objectively assessed secondhand smoke exposure and mental health in adults: cross-sectional and prospective evidence from the Scottish Health Survey | journal = Archives of General Psychiatry | volume = 67 | issue = 8 | pages = 850–5 | date = August 2010 | pmid = 20529994 | doi = 10.1001/archgenpsychiatry.2010.76 | doi-access = free }}</ref>

==== Social and behavioral ====
Medical researchers have found that smoking is a predictor of divorce.<ref name="isbn0-8058-2547-9">{{cite book | vauthors = Bachman JG, Wadsworth KN, O'Malley PM, Johnston LD, Schulenberg JE | title = Smoking, drinking, and drug use in young adulthood: the impacts of new freedoms and new responsibilities | publisher = L. Erlbaum Associates | location = Hillsdale, N.J | year = 1997 | page = [https://archive.org/details/smokingdrinkingd00bach/page/70 70] | isbn = 978-0-8058-2547-3 | url = https://archive.org/details/smokingdrinkingd00bach/page/70 }}</ref> Smokers have a 53% greater chance of divorce than nonsmokers.<ref>{{cite journal | doi = 10.1037/h0089864 | title = Smoke gets in your eyes: Cigarette smoking and divorce in a national sample of American adults | year = 1998 |vauthors=Doherty EW, Doherty WJ | journal = Families, Systems, & Health | volume = 16 | issue = 4 | pages = 393–400 }}</ref>

==== Cognitive function ====
The usage of tobacco can also create cognitive dysfunction. There seems to be an increased risk of [[Alzheimer's disease]] (AD), although "case–control and cohort studies produce conflicting results as to the direction of the association between smoking and AD".<ref name="alzheimer-almeida">{{cite journal | vauthors = Almeida OP, Hulse GK, Lawrence D, Flicker L | title = Smoking as a risk factor for Alzheimer's disease: contrasting evidence from a systematic review of case-control and cohort studies | journal = Addiction | volume = 97 | issue = 1 | pages = 15–28 | date = January 2002 | pmid = 11895267 | doi = 10.1046/j.1360-0443.2002.00016.x | s2cid = 22936675 | url = https://semanticscholar.org/paper/0acb84e7db037da7d071fba720ffb8fa83b09cac }}</ref> Smoking has been found to contribute to dementia and cognitive decline,<ref name="pmid17573335">{{cite journal | vauthors = Anstey KJ, von Sanden C, Salim A, O'Kearney R | title = Smoking as a risk factor for dementia and cognitive decline: a meta-analysis of prospective studies | journal = American Journal of Epidemiology | volume = 166 | issue = 4 | pages = 367–78 | date = August 2007 | pmid = 17573335 | doi = 10.1093/aje/kwm116 | doi-access = free }}</ref> reduced memory and cognitive abilities in adolescents,<ref name="pmid15607301">{{cite journal | vauthors = Jacobsen LK, Krystal JH, Mencl WE, Westerveld M, Frost SJ, Pugh KR | title = Effects of smoking and smoking abstinence on cognition in adolescent tobacco smokers | journal = Biological Psychiatry | volume = 57 | issue = 1 | pages = 56–66 | date = January 2005 | pmid = 15607301 | doi = 10.1016/j.biopsych.2004.10.022 | s2cid = 10146493 }}</ref> and brain shrinkage (cerebral atrophy).<ref>{{cite journal | vauthors = Brody AL, Mandelkern MA, Jarvik ME, Lee GS, Smith EC, Huang JC, Bota RG, Bartzokis G, London ED | title = Differences between smokers and nonsmokers in regional gray matter volumes and densities | journal = Biological Psychiatry | volume = 55 | issue = 1 | pages = 77–84 | date = January 2004 | pmid = 14706428 | doi = 10.1016/S0006-3223(03)00610-3 | s2cid = 25442824 }}</ref><ref>{{cite journal | vauthors = Akiyama H, Meyer JS, Mortel KF, Terayama Y, Thornby JI, Konno S | title = Normal human aging: factors contributing to cerebral atrophy | journal = Journal of the Neurological Sciences | volume = 152 | issue = 1 | pages = 39–49 | date = November 1997 | pmid = 9395125 | doi = 10.1016/S0022-510X(97)00141-X | s2cid = 24676760 }}</ref>

Most notably, some studies have found that patients with Alzheimer's disease are more likely not to have smoked than the general population, which has been interpreted to suggest that smoking offers some protection against Alzheimer's. However, the research in this area is limited and the results are conflicting; some studies show that smoking increases the risk of Alzheimer's disease.<ref>{{cite journal | vauthors = Cataldo JK, Prochaska JJ, Glantz SA | title = Cigarette smoking is a risk factor for Alzheimer's Disease: an analysis controlling for tobacco industry affiliation | journal = Journal of Alzheimer's Disease | volume = 19 | issue = 2 | pages = 465–80 | date = 2010 | pmid = 20110594 | pmc = 2906761 | doi = 10.3233/JAD-2010-1240 }}</ref> A recent review of the available scientific literature concluded that the apparent decrease in Alzheimer's risk may be simply because smokers tend to die before reaching the age at which Alzheimer's normally occurs. "Differential mortality is always likely to be a problem where there is a need to investigate the effects of smoking in a disorder with very low incidence rates before age 75 years, which is the case of Alzheimer's disease," it stated, noting that smokers are only half as likely as non-smokers to survive to the age of 80.<ref name="alzheimer-almeida" />

Some older analyses have claimed that non-smokers are up to twice as likely as smokers to develop Alzheimer's disease.<ref>{{cite journal | vauthors = Fratiglioni L, Wang HX | title = Smoking and Parkinson's and Alzheimer's disease: review of the epidemiological studies | journal = Behavioural Brain Research | volume = 113 | issue = 1–2 | pages = 117–20 | date = August 2000 | pmid = 10942038 | doi = 10.1016/S0166-4328(00)00206-0 | s2cid = 4045868 }}</ref> However, a more current analysis found that most of the studies, which showed a preventing effect, had a close affiliation to the tobacco industry. Researchers without tobacco lobby influence have concluded the complete opposite: Smokers are almost twice as likely as nonsmokers to develop Alzheimer's disease.<ref>{{cite journal | vauthors = Cataldo JK, Prochaska JJ, Glantz SA | title = Cigarette smoking is a risk factor for Alzheimer's Disease: an analysis controlling for tobacco industry affiliation | journal = Journal of Alzheimer's Disease | volume = 19 | issue = 2 | pages = 465–80 | date = Jul 2010 | pmid = 20110594 | pmc = 2906761 | doi = 10.3233/JAD-2010-1240 }}</ref>

Former and current smokers have a lower incidence of [[Parkinson's disease]] compared to people who have never smoked,<ref>{{cite journal | vauthors = Allam MF, Campbell MJ, Hofman A, Del Castillo AS, Fernández-Crehuet Navajas R | title = Smoking and Parkinson's disease: systematic review of prospective studies | journal = Movement Disorders | volume = 19 | issue = 6 | pages = 614–21 | date = June 2004 | pmid = 15197698 | doi = 10.1002/mds.20029 | s2cid = 36001133 }}</ref><ref>{{cite journal | vauthors = Allam MF, Campbell MJ, Del Castillo AS, Fernández-Crehuet Navajas R | title = Parkinson's disease protects against smoking? | journal = Behavioural Neurology | volume = 15 | issue = 3–4 | pages = 65–71 | year = 2004 | pmid = 15706049 | pmc = 5488608 | doi = 10.1155/2004/516302 | doi-access = free }}</ref> although the authors stated that it was more likely that the movement disorders which are part of Parkinson's disease prevented people from being able to smoke than that smoking itself was protective. Another study considered a possible role of nicotine in reducing Parkinson's risk: nicotine stimulates the [[dopaminergic]] system of the brain, which is damaged in Parkinson's disease, while other compounds in tobacco smoke inhibit [[Monoamine oxidase B|MAO-B]], an enzyme which produces oxidative radicals by breaking down dopamine.<ref>{{cite journal | vauthors = Quik M | title = Smoking, nicotine and Parkinson's disease | journal = Trends in Neurosciences | volume = 27 | issue = 9 | pages = 561–8 | date = September 2004 | pmid = 15331239 | doi = 10.1016/j.tins.2004.06.008 | s2cid = 42385863 }}</ref>

In many respects, [[nicotine]] acts on the nervous system in a similar way to [[caffeine]]. Some writings have stated that smoking can also increase [[mental concentration]]; one study documents a significantly better performance on the normed [[Raven's Progressive Matrices|Advanced Raven Progressive Matrices test]] after smoking.<ref name="pmid7892431">{{cite journal | vauthors = Stough C, Mangan G, Bates T, Pellett O | title = Smoking and Raven IQ | journal = Psychopharmacology | volume = 116 | issue = 3 | pages = 382–4 | date = November 1994 | pmid = 7892431 | doi = 10.1007/BF02245346 | s2cid = 19155259 }}</ref>

Most smokers, when denied access to nicotine, exhibit withdrawal symptoms such as irritability, jitteriness, [[Xerostomia|dry mouth]], and rapid heart beat.<ref name="Why people smoke">{{cite journal | vauthors = Jarvis MJ | title = Why people smoke | journal = BMJ | volume = 328 | issue = 7434 | pages = 277–9 | date = January 2004 | pmid = 14751901 | pmc = 324461 | doi = 10.1136/bmj.328.7434.277 }}</ref> The onset of these symptoms is very fast, nicotine's half-life being only two hours.<ref>{{Cite web|url=https://www.mayomedicallaboratories.com/test-catalog/Clinical+and+Interpretive/82510|title=NICOU - Clinical: Nicotine and Metabolites, Urine|website=www.mayomedicallaboratories.com|access-date=2018-01-03}}</ref> The [[Psychology|psychological]] dependence may linger for months or even many years. Unlike some [[recreational drug use|recreational drugs]], nicotine does not measurably alter a smoker's [[motor skill]]s, [[judgement]], or [[language]] abilities while under the influence of the drug. Tobacco withdrawal has been shown to cause clinically significant distress.<ref>{{cite journal | vauthors = Hughes JR | title = Clinical significance of tobacco withdrawal | journal = Nicotine & Tobacco Research | volume = 8 | issue = 2 | pages = 153–6 | date = April 2006 | pmid = 16766409 | doi = 10.1080/14622200500494856 }}</ref>

{{Self-contradictory|about=schizophrenia; the following para contradicts the history of claimed benefits section|date=October 2022}}
A very large percentage of [[Schizophrenia and smoking|schizophrenics]] smoke tobacco as a form of self-medication.<ref name="mcneill">{{Cite report |vauthors=McNeill A |url=https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.622.6748&rep=rep1&type=pdf |title=Smoking and mental health – a review of the literature |date=December 2001 |publisher=SmokeFree London Programme | citeseerx=10.1.1.622.6748 |access-date=2008-10-05 |archive-url=https://web.archive.org/web/20220307072130/https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.622.6748&rep=rep1&type=pdf |archive-date=7 March 2022 }}</ref><ref name="ocps">{{Cite book |vauthors=Meltzer H, Gill B, Petticrew M, Hinds K | title = OPCS Surveys of Psychiatric Morbidity Report 3: Economic Activity and Social Functioning of Adults With Psychiatric Disorders | publisher = London, Her Majesty's Stationery Office | year = 1995}}{{Page needed|date=May 2012}}</ref><ref name="kelly_mccreadie">{{cite journal | vauthors = Kelly C, McCreadie RG | title = Smoking habits, current symptoms, and premorbid characteristics of schizophrenic patients in Nithsdale, Scotland | journal = The American Journal of Psychiatry | volume = 156 | issue = 11 | pages = 1751–7 | date = November 1999 | pmid = 10553739 | doi = 10.1176/ajp.156.11.1751 | s2cid = 23987972 }}</ref><ref name="hughes_et_al">{{cite journal | vauthors = Hughes JR, Hatsukami DK, Mitchell JE, Dahlgren LA | title = Prevalence of smoking among psychiatric outpatients | journal = The American Journal of Psychiatry | volume = 143 | issue = 8 | pages = 993–7 | date = August 1986 | pmid = 3487983 | doi = 10.1176/ajp.143.8.993 | citeseerx = 10.1.1.470.8010 }}</ref> The high rate of tobacco use by the mentally ill is a major factor in their decreased life expectancy, which is about 25 years shorter than the general population.<ref>{{cite journal | vauthors = Schroeder SA | title = Shattuck Lecture. We can do better—improving the health of the American people | journal = The New England Journal of Medicine | volume = 357 | issue = 12 | pages = 1221–8 | date = September 2007 | pmid = 17881753 | doi = 10.1056/NEJMsa073350 | s2cid = 12299551 | url = https://semanticscholar.org/paper/21cce2df36ea35f7be8f03d193eacd898917a71c }}</ref> Following the observation that smoking improves condition of people with schizophrenia, in particular working memory deficit, [[nicotine patch]]es had been proposed as a way to treat schizophrenia.<ref name="url_Schizophrenia_Smoking">{{cite web | url =http://www.abc.net.au/rn/healthreport/stories/2002/614060.htm | title = Schizophrenia and Smoking | vauthors = George T |date = 2002-07-22 | work = Health Report | publisher = ABC Radio National (Australian Broadcasting Corporation) |access-date = 2012-05-06 }}</ref> Some studies suggest that a link exists between smoking and mental illness, citing the high incidence of smoking amongst those with [[schizophrenia]]<ref>{{cite journal | vauthors = Sacco KA, Bannon KL, George TP | title = Nicotinic receptor mechanisms and cognition in normal states and neuropsychiatric disorders | journal = Journal of Psychopharmacology | volume = 18 | issue = 4 | pages = 457–74 | date = December 2004 | pmid = 15582913 | pmc = 1201375 | doi = 10.1177/0269881104047273 }}</ref> and the possibility that smoking may alleviate some of the symptoms of mental illness,<ref>{{cite journal | vauthors = Kumari V, Postma P | title = Nicotine use in schizophrenia: the self medication hypotheses | journal = Neuroscience and Biobehavioral Reviews | volume = 29 | issue = 6 | pages = 1021–34 | year = 2005 | pmid = 15964073 | doi = 10.1016/j.neubiorev.2005.02.006 | s2cid = 15581894 }}</ref> but these have not been conclusive. In 2015, a meta-analysis found that smokers were at greater risk of developing psychotic illness.<ref>{{cite journal | vauthors = Gurillo P, Jauhar S, Murray RM, MacCabe JH | title = Does tobacco use cause psychosis? Systematic review and meta-analysis | journal = The Lancet. Psychiatry | volume = 2 | issue = 8 | pages = 718–725 | date = August 2015 | pmid = 26249303 | pmc = 4698800 | doi = 10.1016/S2215-0366(15)00152-2 }}</ref>

Recent studies have linked smoking to anxiety disorders, suggesting the correlation (and possibly mechanism) may be related to the broad class of anxiety disorders, and not limited to just depression. Current and ongoing research attempt to explore the addiction-anxiety relationship. Data from multiple studies suggest that anxiety disorders and depression play a role in cigarette smoking.<ref name="pmid2395193">{{cite journal | vauthors = Anda RF, Williamson DF, Escobedo LG, Mast EE, Giovino GA, Remington PL | title = Depression and the dynamics of smoking. A national perspective | journal = JAMA | volume = 264 | issue = 12 | pages = 1541–5 | date = September 1990 | pmid = 2395193 | doi = 10.1001/jama.1990.03450120053028 }}</ref> A history of regular smoking was observed more frequently among individuals who had experienced a [[major depressive disorder]] at some time in their lives than among individuals who had never experienced major depression or among individuals with no psychiatric diagnosis.<ref name="pmid2395194">{{cite journal | vauthors = Glassman AH, Helzer JE, Covey LS, Cottler LB, Stetner F, Tipp JE, Johnson J | title = Smoking, smoking cessation, and major depression | journal = JAMA | volume = 264 | issue = 12 | pages = 1546–9 | date = September 1990 | pmid = 2395194 | doi = 10.1001/jama.1990.03450120058029 }}</ref> People with major depression are also much less likely to [[smoking cessation|quit]] due to the increased risk of experiencing mild to severe states of depression, including a major depressive episode.<ref>{{cite journal | vauthors = Covey LS, Glassman AH, Stetner F | title = Cigarette smoking and major depression | journal = Journal of Addictive Diseases | volume = 17 | issue = 1 | pages = 35–46 | year = 1998 | pmid = 9549601 | doi = 10.1300/J069v17n01_04 }}</ref> Depressed smokers appear to experience more withdrawal symptoms on quitting, are less likely to be successful at quitting, and are more likely to relapse.<ref>{{cite journal | vauthors = Hall SM, Muñoz RF, Reus VI, Sees KL | title = Nicotine, negative affect, and depression | journal = Journal of Consulting and Clinical Psychology | volume = 61 | issue = 5 | pages = 761–7 | date = October 1993 | pmid = 7902368 | doi = 10.1037/0022-006X.61.5.761 }}</ref>

=== Pregnancy ===
{{anchor#Reproductive}}
{{Main|Smoking and pregnancy}}
A number of studies have shown that tobacco use is a significant factor in [[miscarriage]]s among [[Pregnancy|pregnant]] smokers, and that it contributes to a number of other threats to the health of the fetus. It slightly increases the risk of [[neural tube defects]].<ref>{{cite journal | vauthors = Wang M, Wang ZP, Gong R, Zhao ZT | title = Maternal smoking during pregnancy and neural tube defects in offspring: a meta-analysis | journal = Child's Nervous System | volume = 30 | issue = 1 | pages = 83–9 | date = January 2014 | pmid = 23760473 | doi = 10.1007/s00381-013-2194-5 | s2cid = 40996359 }}</ref>

Environmental tobacco smoke exposure and maternal smoking during pregnancy have been shown to cause lower infant birth weights.<ref name="pmid17506887">{{cite journal | vauthors = Ward C, Lewis S, Coleman T | title = Prevalence of maternal smoking and environmental tobacco smoke exposure during pregnancy and impact on birth weight: retrospective study using Millennium Cohort | journal = BMC Public Health | volume = 7 | pages = 81 | date = May 2007 | pmid = 17506887 | pmc = 1884144 | doi = 10.1186/1471-2458-7-81 }}</ref>

Studies have shown an association between prenatal exposure to environmental tobacco smoke and conduct disorder in children.{{medcn|date=March 2018}} As well, post-natal tobacco smoke exposure may cause similar behavioral problems in children.{{medcn|date=March 2018}}

=== Drug interactions ===

Smoking is known to increase levels of liver enzymes that break down drugs and toxins. That means that drugs cleared by these enzymes are cleared more quickly in smokers, which may result in the drugs not working. Specifically, levels of CYP1A2 and CYP2A6 are induced:<ref>{{cite journal | vauthors = Kroon LA | title = Drug interactions with smoking | journal = American Journal of Health-System Pharmacy | volume = 64 | issue = 18 | pages = 1917–21 | date = September 2007 | pmid = 17823102 | doi = 10.2146/ajhp060414 | s2cid = 5397510 | url = https://semanticscholar.org/paper/f5403b54c42ec12a243809f7f3a92f596d4e8354 }}</ref><ref>{{cite journal | vauthors = Ande A, McArthur C, Ayuk L, Awasom C, Achu PN, Njinda A, Sinha N, Rao PS, Agudelo M, Nookala AR, Simon S, Kumar A, Kumar S | title = Effect of mild-to-moderate smoking on viral load, cytokines, oxidative stress, and cytochrome P450 enzymes in HIV-infected individuals | journal = PLOS ONE | volume = 10 | issue = 4 | pages = e0122402 | year = 2015 | pmid = 25879453 | pmc = 4399877 | doi = 10.1371/journal.pone.0122402 | bibcode = 2015PLoSO..1022402A | doi-access = free }}</ref> substrates for 1A2 include [[caffeine]] and tricyclic antidepressants such as [[amitriptyline]]; substrates for 2A6 include the anticonvulsant [[valproic acid]].

=== Multigenerational effects ===
{{Main|Epigenetic effects of smoking}}

=== Other harm ===
{{See also|Women and smoking#Unique gender differences and health effects for women}}
[[File:Protein AZGP1 PDB 1t7v.png|thumb|Protein AZGP1]]
Studies suggest that smoking decreases appetite, but did not conclude that overweight people should smoke or that their health would improve by smoking. This is also a cause of heart diseases.<ref name="pmid15508020">{{Cite journal |vauthors=Chen H, Vlahos R, Bozinovski S, Jones J, Anderson GP, Morris MJ |date=April 2005 |title=Effect of short-term cigarette smoke exposure on body weight, appetite and brain neuropeptide Y in mice |journal=Neuropsychopharmacology |volume=30 |issue=4 |pages=713–9 |doi=10.1038/sj.npp.1300597 |pmid=15508020 |doi-access=free}}</ref><ref name="lay news medical">{{cite news |title=Cigarette smoking can dramatically affect appetite and weight control |url=https://www.news-medical.net/news/2004/11/01/5991.aspx |access-date=6 October 2022 |work=News-Medical |date=1 November 2004 |archive-url=https://web.archive.org/web/20220604051618/https://www.news-medical.net/news/2004/11/01/5991.aspx |archive-date=4 June 2022}}</ref> Smoking also decreases weight by overexpressing the gene [[AZGP1]], which stimulates [[lipolysis]].<ref name=smoking>{{cite journal | vauthors = Vanni H, Kazeros A, Wang R, Harvey BG, Ferris B, De BP, Carolan BJ, Hübner RH, O'Connor TP, Crystal RG | title = Cigarette smoking induces overexpression of a fat-depleting gene AZGP1 in the human | journal = Chest | volume = 135 | issue = 5 | pages = 1197–1208 | date = May 2009 | pmid = 19188554 | pmc = 2679098 | doi = 10.1378/chest.08-1024 }}</ref>

Smoking causes about 10% of the global burden of fire deaths,<ref name="pmid10938207">{{cite journal | vauthors = Leistikow BN, Martin DC, Milano CE | title = Fire injuries, disasters, and costs from cigarettes and cigarette lights: a global overview | journal = Preventive Medicine | volume = 31 | issue = 2 Pt 1 | pages = 91–9 | date = August 2000 | pmid = 10938207 | doi = 10.1006/pmed.2000.0680 | s2cid = 11722177 | url = https://semanticscholar.org/paper/a1c64847591749ed01f54662eec4ac441b2a24cf }}</ref> and smokers are placed at an increased risk of injury-related deaths in general, partly due to also experiencing an increased risk of dying in a motor vehicle crash.<ref name="pmid11144627">{{cite journal | vauthors = Leistikow BN, Martin DC, Samuels SJ | title = Injury death excesses in smokers: a 1990–95 United States national cohort study | journal = Injury Prevention | volume = 6 | issue = 4 | pages = 277–80 | date = December 2000 | pmid = 11144627 | pmc = 1730660 | doi = 10.1136/ip.6.4.277 }}</ref>

Smoking increases the risk of symptoms associated with [[Crohn's disease]] (a dose-dependent effect with use of greater than 15 cigarettes per day).<ref name="pmid10571595">{{cite journal | vauthors = Cosnes J, Carbonnel F, Carrat F, Beaugerie L, Cattan S, Gendre J | title = Effects of current and former cigarette smoking on the clinical course of Crohn's disease | journal = Alimentary Pharmacology & Therapeutics | volume = 13 | issue = 11 | pages = 1403–11 | date = November 1999 | pmid = 10571595 | doi = 10.1046/j.1365-2036.1999.00630.x | s2cid = 6620451 }}</ref><ref name="pmid2598752">{{cite journal | vauthors = Calkins BM | title = A meta-analysis of the role of smoking in inflammatory bowel disease | journal = Digestive Diseases and Sciences | volume = 34 | issue = 12 | pages = 1841–54 | date = December 1989 | pmid = 2598752 | doi = 10.1007/BF01536701 | s2cid = 5775169 }}</ref><ref name="pmid18069751">{{cite journal | vauthors = Lakatos PL, Szamosi T, Lakatos L | title = Smoking in inflammatory bowel diseases: good, bad or ugly? | journal = World Journal of Gastroenterology | volume = 13 | issue = 46 | pages = 6134–9 | date = December 2007 | pmid = 18069751 | pmc = 4171221 | doi = 10.3748/wjg.13.6134 }}</ref><ref name="Cite pmid|17120402">{{cite journal | vauthors = Mahid SS, Minor KS, Soto RE, Hornung CA, Galandiuk S | title = Smoking and inflammatory bowel disease: a meta-analysis | journal = Mayo Clinic Proceedings | volume = 81 | issue = 11 | pages = 1462–71 | date = November 2006 | pmid = 17120402 | doi = 10.4065/81.11.1462 }}</ref> There is some evidence for decreased rates of [[endometriosis]] in infertile smoking women,<ref>{{cite journal | vauthors = Missmer SA, Hankinson SE, Spiegelman D, Barbieri RL, Marshall LM, Hunter DJ | title = Incidence of laparoscopically confirmed endometriosis by demographic, anthropometric, and lifestyle factors | journal = American Journal of Epidemiology | volume = 160 | issue = 8 | pages = 784–96 | date = October 2004 | pmid = 15466501 | doi = 10.1093/aje/kwh275 | first6 = D. | doi-access = free }}</ref> although other studies have found that smoking increases the risk in infertile women.<ref>{{cite journal | vauthors = Calhaz-Jorge C, Mol BW, Nunes J, Costa AP | title = Clinical predictive factors for endometriosis in a Portuguese infertile population | journal = Human Reproduction | volume = 19 | issue = 9 | pages = 2126–31 | date = September 2004 | pmid = 15229202 | doi = 10.1093/humrep/deh374 | doi-access = free }}</ref> There is little or no evidence of a protective effect in fertile women. Some preliminary data from 1996 suggested a reduced incidence of [[uterine fibroids]],<ref>{{cite journal | vauthors = Baron JA | title = Beneficial effects of nicotine and cigarette smoking: the real, the possible and the spurious | journal = British Medical Bulletin | volume = 52 | issue = 1 | pages = 58–73 | date = January 1996 | pmid = 8746297 | doi = 10.1093/oxfordjournals.bmb.a011533 | doi-access = free }}</ref> but overall the evidence is unconvincing.<ref name="pmid11035989">{{cite journal | vauthors = Schwartz SM, Marshall LM, Baird DD | title = Epidemiologic contributions to understanding the etiology of uterine leiomyomata | journal = Environmental Health Perspectives | volume = 108 | issue = Suppl 5 | pages = 821–7 | date = October 2000 | pmid = 11035989 | doi = 10.1289/ehp.00108s5821 | jstor = 3454313 | doi-access = free }}</ref>

Current research shows that tobacco smokers who are exposed to residential radon are twice as likely to develop lung cancer as non-smokers.<ref name="pmid7997518">{{cite journal | vauthors = Lubin JH, Steindorf K | title = Cigarette use and the estimation of lung cancer attributable to radon in the United States | journal = Radiation Research | volume = 141 | issue = 1 | pages = 79–85 | date = January 1995 | pmid = 7997518 | doi = 10.2307/3579093 | jstor = 3579093 | bibcode = 1995RadR..141...79L }}</ref> As well, the risk of developing lung cancer from asbestos exposure is twice as likely for smokers than for non-smokers.<ref name="pmid16849527">{{cite journal | vauthors = Reid A, de Klerk NH, Ambrosini GL, Berry G, Musk AW | title = The risk of lung cancer with increasing time since ceasing exposure to asbestos and quitting smoking | journal = Occupational and Environmental Medicine | volume = 63 | issue = 8 | pages = 509–12 | date = August 2006 | pmid = 16849527 | pmc = 2078130 | doi = 10.1136/oem.2005.025379 }}</ref>

New research has found that women who smoke are at significantly increased risk of developing an [[abdominal aortic aneurysm]], a condition in which a weak area of the [[Abdomen|abdominal]] [[aorta]] expands or bulges, and is the most common form of [[aortic aneurysm]].<ref name="pmid18854591">{{cite journal | vauthors = Lederle FA, Larson JC, Margolis KL, Allison MA, Freiberg MS, Cochrane BB, Graettinger WF, Curb JD | title = Abdominal aortic aneurysm events in the women's health initiative: cohort study | journal = BMJ | volume = 337 | pages = a1724 | date = October 2008 | pmid = 18854591 | pmc = 2658825 | doi = 10.1136/bmj.a1724 | url = http://www.medicalnewstoday.com/articles/125908.php }}</ref>

Smoking leads to an increased risk of [[bone fracture]]s, especially [[hip fracture]]s.<ref name = "pmid15175845">{{cite journal | vauthors = Kanis JA, Johnell O, Oden A, Johansson H, De Laet C, Eisman JA, Fujiwara S, Kroger H, McCloskey EV, Mellstrom D, Melton LJ, Pols H, Reeve J, Silman A, Tenenhouse A | title = Smoking and fracture risk: a meta-analysis | journal = Osteoporosis International | volume = 16 | issue = 2 | pages = 155–62 | date = February 2005 | pmid = 15175845 | doi = 10.1007/s00198-004-1640-3 | s2cid = 19890259 }}</ref> It also leads to slower [[wound healing]] after surgery, and an increased rate of postoperative healing complication.<ref name = "pmid22508785">{{cite journal | vauthors = Sørensen LT | title = Wound healing and infection in surgery. The clinical impact of smoking and smoking cessation: a systematic review and meta-analysis | journal = Archives of Surgery | volume = 147 | issue = 4 | pages = 373–83 | date = April 2012 | pmid = 22508785 | doi = 10.1001/archsurg.2012.5 | doi-access = free }}</ref>

Tobacco smokers are 30-40% more likely to develop [[diabetes mellitus|type 2 diabetes]] than non-smokers, and the risk increases with the number of cigarettes smoked. Furthermore, diabetic smokers have worse outcomes than diabetic non-smokers.<ref>{{cite web |title=Smoking and Diabetes |url=https://www.cdc.gov/tobacco/campaign/tips/diseases/diabetes.html |website=Centers for Disease Control and Prevention |language=en-us |date=23 April 2018}}</ref><ref>{{cite web |title=2014 Surgeon General's Report: The Health Consequences of Smoking—50 Years of Progress |url=https://www.cdc.gov/tobacco/data_statistics/sgr/50th-anniversary/index.htm |website=Centers for Disease Control and Prevention |language=en-us |date=5 March 2018}}</ref>

=== Claimed benefits ===
{{anchor|Smoker's paradox}}
Against the background of the overwhelmingly negative effects of smoking on health, some [[observational studies]] have suggested that smoking might have specific beneficial effects, including in the field of [[cardiovascular disease]].<ref name=Li2019/><ref name=Usman2020/> Interest in this [[epidemiological]] phenomenon has also been aroused by [[COVID-19]].<ref name=Usman2020/> [[Systematic review]] of reports that suggested smokers respond better to treatment for [[ischemic stroke]] provided no support for such claims.<ref name=Li2019/>

Claims of surprising benefits of smoking, based on observational data, have also been made for [[Parkinson's disease]],<ref name=Usman2020/> as well as a variety of other conditions, including [[basal-cell carcinoma]],<ref name="Arafa2020">{{cite journal | vauthors = Arafa A, Mostafa A, Navarini AA, Dong JY | title = The association between smoking and risk of skin cancer: a meta-analysis of cohort studies | journal = Cancer Causes & Control | volume = 31 | issue = 8 | pages = 787–794 | date = August 2020 | pmid = 32458137 | doi = 10.1007/s10552-020-01319-8 | s2cid = 218898153 }}</ref> [[malignant melanoma]],<ref name="Arafa2020" /> [[acute mountain sickness]],<ref>{{cite journal | vauthors = Xu C, Lu HX, Wang YX, Chen Y, Yang SH, Luo YJ | title = Association between smoking and the risk of acute mountain sickness: a meta-analysis of observational studies | journal = Military Medical Research | volume = 3 | pages = 37 | date = 2016 | pmid = 27980800 | pmc = 5146861 | doi = 10.1186/s40779-016-0108-z }}</ref> [[pemphigus]],<ref>{{cite journal | vauthors = Lai O, Recke A, Zillikens D, Kasperkiewicz M | title = Influence of cigarette smoking on pemphigus - a systematic review and pooled analysis of the literature | journal = Journal of the European Academy of Dermatology and Venereology | volume = 32 | issue = 8 | pages = 1256–1262 | date = August 2018 | pmid = 29478302 | doi = 10.1111/jdv.14886 | s2cid = 3830347 }}</ref> [[Celiac Disease|celiac disease]],<ref>{{cite journal | vauthors = Wijarnpreecha K, Lou S, Panjawatanan P, Cheungpasitporn W, Pungpapong S, Lukens FJ, Ungprasert P | title = Cigarette smoking and risk of celiac disease: A systematic review and meta-analysis | journal = United European Gastroenterology Journal | volume = 6 | issue = 9 | pages = 1285–1293 | date = November 2018 | pmid = 30386601 | pmc = 6206527 | doi = 10.1177/2050640618786790 }}</ref> and [[ulcerative colitis]],<ref name="To2016">{{cite journal | vauthors = To N, Ford AC, Gracie DJ | title = Systematic review with meta-analysis: the effect of tobacco smoking on the natural history of ulcerative colitis | journal = Alimentary Pharmacology & Therapeutics | volume = 44 | issue = 2 | pages = 117–26 | date = July 2016 | pmid = 27193202 | doi = 10.1111/apt.13663 | doi-access = free }}</ref> among others.<ref>{{cite journal | vauthors = Hopper CP, Zambrana PN, Goebel U, Wollborn J | title = A brief history of carbon monoxide and its therapeutic origins | journal = Nitric Oxide | volume = 111–112 | pages = 45–63 | date = June 2021 | pmid = 33838343 | doi = 10.1016/j.niox.2021.04.001| issn=1089-8603  | s2cid = 233205099 }}</ref>

Tobacco smoke has many bioactive substances, including [[nicotine]], that are capable of exerting a variety of [[Systemic disease|systemic]] effects.<ref name=Usman2020/> Surprising correlations [[Correlation does not imply causation|may also stem]] from non-biological factors such as [[residual confounding]] (that is to say, the methodological difficulties in completely adjusting for every confounding factor that can affect outcomes in observational studies).<ref name=Usman2020 />

==== In Parkinson's disease ====
In the case of Parkinson's disease, a series of observational studies that consistently suggest a possibly substantial reduction in risk among smokers (and other consumers of [[tobacco]] products) has led to longstanding interest among epidemiologists.<ref name="Chen2018">{{cite journal |vauthors=Chen H |title=The changing landscape of Parkinson epidemiologic research |journal=Journal of Parkinson's Disease |volume=8 |issue=1 |pages=1–12 |date=2018 |pmid=29154293 |pmc=5836408 |doi=10.3233/JPD-171238 |doi-access=free}}</ref><ref name="Kouli2018">{{cite book|title=Parkinson's Disease: Pathogenesis and Clinical Aspects [Internet] |vauthors=Kouli A, Torsney KM, Kuan WL |date=2018 |publisher=Codon publications |isbn=9780994438164 |veditors=Stoker TB, Greenland JC |location=Brisbane |chapter=Parkinson's Disease: Etiology, neuropathology, and pathogenesis |doi=10.15586/codonpublications.parkinsonsdisease.2018 |pmid=30702842 |doi-access=free}}</ref><ref name="Martino2017">{{cite journal |vauthors=Martino R, Candundo H, Lieshout PV, Shin S, Crispo JA, Barakat-Haddad C |date=2017 |title=Onset and progression factors in Parkinson's disease: a systematic review |journal=Neurotoxicology |volume=61 |pages=132–141 |doi=10.1016/j.neuro.2016.04.003 |pmid=27058967 |s2cid=31774312}}</ref><ref name="Breckenridge2016">{{cite journal |vauthors=Breckenridge CB, Berry C, Chang ET, Sielken RL, Mandel JS |date=2016 |title=Association between Parkinson's disease and cigarette smoking, rural living, well-water consumption, farming and pesticide use: systematic review and meta-analysis |journal=PLOS ONE |volume=11 |issue=4 |pages=e0151841 |bibcode=2016PLoSO..1151841B |doi=10.1371/journal.pone.0151841 |pmc=4824443 |pmid=27055126 |doi-access=free}}</ref> Non-biological factors that may contribute to such observations include reverse [[causality]] (whereby [[prodromal]] symptoms of Parkinson's disease may lead some smokers to quit before diagnosis), and personality considerations (people predisposed to Parkinson's disease tend to be relatively [[Risk aversion (psychology)|risk-averse]], and may be less likely to have a history of smoking).<ref name="Chen2018" /> Possible existence of a biological effect is supported by a few studies that involved low levels of exposure to nicotine without any active smoking.<ref name="Chen2018" /> A data-driven hypothesis that long-term administration of very low doses of nicotine (for example, in an ordinary diet) might provide a degree of [[Neuroprotection|neurological protection]] against Parkinson's disease remains open as a potential [[Preventive healthcare|preventive]] strategy.<ref name="Chen2018" /><ref name="Ascherio2016">{{cite journal |vauthors=Ascherio A, Schwarzschild MA |date=2016 |title=The epidemiology of Parkinson's disease: risk factors and prevention |url= |journal=The Lancet. Neurology |volume=15 |issue=12 |pages=1257–1272 |doi=10.1016/S1474-4422(16)30230-7 |pmid=27751556 |s2cid=19994300}}</ref><ref name="Oertel2016">{{cite journal |vauthors=Oertel W, Schulz JB|date=October 2016 |title=Current and experimental treatments of Parkinson disease: a guide for neuroscientists |url= |journal=Journal of Neurochemistry |volume=139 | issue = Suppl 1 |pages=325–337 |doi=10.1111/jnc.13750 |pmid=27577098 |s2cid=30497369}}</ref><ref name="Ma2017">{{cite journal|vauthors=Ma C, Liu Y, Neumann S, Gao X |date=2017 |title=Nicotine from cigarette smoking and diet and Parkinson disease: a review|journal=Translational Neurodegeneration |volume=6 |issue=|pages=18 |doi=10.1186/s40035-017-0090-8 |pmc=5494127 |pmid=28680589 |doi-access=free}}</ref>

==== History of claimed benefits ====
In 1888, an article appeared in [[Scientific American]] discussing potential [[germicidal]] activity of tobacco smoke providing immunity against [[yellow fever]] [https://www.thejaxsonmag.com/article/yellow-jax-the-1888-jacksonville-yellow-fever-epidemic/ epidemic of Florida] inspiring research in the lab of [[Vincenzo Tassinari]] at the Hygienic Institute of the [[University of Pisa]], who explored the antimicrobial activity against pathogens including [[Bacillus anthracis]], [[Tubercle bacillus]], [[Bacillus prodigiosus]], [[Staphylococcus aureus]], and others.<ref>{{Cite book|url=https://books.google.com/books?id=Mps0AQAAMAAJ&q=viaud+grand+marius+cleopatra+carbonic+oxide&pg=PA35|title=Scientific American|date=1888-11-10|publisher=Munn & Company|pages=296|language=en}}</ref> [[Carbon monoxide]] is a bioactive component tobacco smoke that has been explored for its antimicrobial properties against many of these pathogens.<ref>{{cite journal | vauthors = Hopper CP, De La Cruz LK, Lyles KV, Wareham LK, Gilbert JA, Eichenbaum Z, Magierowski M, Poole RK, Wollborn J, Wang B | display-authors = 6 | title = Role of Carbon Monoxide in Host-Gut Microbiome Communication | journal = Chemical Reviews | volume = 120 | issue = 24 | pages = 13273–13311 | date = December 2020 | pmid = 33089988 | doi = 10.1021/acs.chemrev.0c00586 | s2cid = 224824871 }}</ref>

On epidemiological grounds, unexpected correlations between smoking and favorable outcomes initially emerged in the context of cardiovascular disease, where they were described as a '''smoker's paradox''' (or '''smoking paradox''').<ref name="Usman2020">{{cite journal | vauthors = Usman MS, Siddiqi TJ, Khan MS, Patel UK, Shahid I, Ahmed J, Kalra A, Michos ED | display-authors = 6 | title = Is there a smoker's paradox in COVID-19? | journal = BMJ Evidence-Based Medicine | pages = bmjebm–2020–111492 | date = August 2020 | volume = 26 | issue = 6 | pmid = 32788164 | doi = 10.1136/bmjebm-2020-111492 | doi-access = free }}</ref><ref name="Li2019">{{cite journal | vauthors = Li B, Li D, Liu JF, Wang L, Li BZ, Yan XJ, Liu W, Wu K, Xiang RL | display-authors = 6 | title = "Smoking paradox" is not true in patients with ischemic stroke: a systematic review and meta-analysis | journal = Journal of Neurology | volume = 268 | issue = 6 | pages = 2042–2054 | date = June 2021 | pmid = 31664548 | pmc = 8179908 | doi = 10.1007/s00415-019-09596-3 | doi-access = free }}</ref> The term ''smoker's paradox'' was coined in 1995 in relation to reports that smokers appeared to have unexpectedly good short-term outcomes following [[acute coronary syndrome]] or stroke.<ref name="Usman2020" /> One of the first reports of an apparent smoker's paradox was published in 1968 based on an observation of relatively decreased mortality in smokers one month after experiencing [[Acute Myocardial Infarction|acute myocardial infarction]].<ref>{{cite journal | vauthors = Weinblatt E, Shapiro S, Frank CW, Sager RV | title = Prognosis of men after first myocardial infarction: mortality and first recurrence in relation to selected parameters | journal = American Journal of Public Health and the Nation's Health | volume = 58 | issue = 8 | pages = 1329–47 | date = August 1968 | pmid = 5691369 | pmc = 1228764 | doi = 10.2105/AJPH.58.8.1329 }}</ref> In the same year, a [[case–control study]] first suggested a possible protective role in Parkinson's disease.<ref name="Chen2018" /><ref name="Nefzger1968">{{cite journal | vauthors = Nefzger MD, Quadfasel FA, Karl VC | title = A retrospective study of smoking in Parkinson's disease | journal = American Journal of Epidemiology | volume = 88 | issue = 2 | pages = 149–58 | date = September 1968 | pmid = 5673487 | doi = 10.1093/oxfordjournals.aje.a120874 }}</ref>

Historical claims of possible benefits [[Schizophrenia and tobacco smoking|in schizophrenia]], whereby smoking was thought to ameliorate [[Schizophrenia#Cognitive symptoms|cognitive symptoms]], are not supported by current evidence.<ref name="Sagud2019">{{cite journal | vauthors = Sagud M, Mihaljevic Peles A, Pivac N | title = Smoking in schizophrenia: recent findings about an old problem | journal = Current Opinion in Psychiatry | volume = 32 | issue = 5 | pages = 402–408 | date = September 2019 | pmid = 31135490 | doi = 10.1097/YCO.0000000000000529 | s2cid = 167219141 | url = http://fulir.irb.hr/6089/ }}</ref><ref name=Coustals2020>{{cite journal | vauthors = Coustals N, Martelli C, Brunet-Lecomte M, Petillion A, Romeo B, Benyamina A | title = Chronic smoking and cognition in patients with schizophrenia: A meta-analysis | journal = Schizophrenia Research | volume = 222 | issue =  | pages = 113–121 | date = August 2020 | pmid = 32507373 | doi = 10.1016/j.schres.2020.03.071 | s2cid = 219300105 | url = https://hal.archives-ouvertes.fr/hal-03493258/file/S0920996420301821.pdf }}</ref>

== Mechanism ==
{{See also|List of additives in cigarettes}}

=== Chemical carcinogens ===
{{See also|List of cigarette smoke carcinogens}}
{{Multiple image|direction=vertical|align=right|image1=Benzopyrene diol epoxide chemical structure.png|image2=Benzopyrene DNA adduct 1JDG.png|width=200|caption1=Benzopyrene diol epoxide, an extremely carcinogenic (cancer-causing) metabolite of benzopyrene, a polycyclic aromatic hydrocarbon produced by burning tobacco|caption2=Benzopyrene, a major mutagen in tobacco smoke, in an [[adduct]] to DNA<ref name="pmid11352722">{{cite journal | vauthors = Pradhan P, Tirumala S, Liu X, Sayer JM, Jerina DM, Yeh HJ | title = Solution structure of a trans-opened (10S)-dA adduct of (+)-(7S,8R,9S,10R)-7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene in a fully complementary DNA duplex: evidence for a major syn conformation | journal = Biochemistry | volume = 40 | issue = 20 | pages = 5870–81 | date = May 2001 | pmid = 11352722 | doi = 10.1021/bi002896q }}</ref>}}

Smoke, or any partially burnt organic matter, contains [[carcinogen]]s (cancer-causing agents). The potential effects of smoking, such as lung cancer, can take up to 20 years to manifest themselves. Historically, women began smoking ''en masse'' later than men, so an increased death rate caused by smoking amongst women did not appear until later. The male lung cancer death rate decreased in 1975 — roughly 20 years after the initial decline in cigarette consumption in men. A fall in consumption in women also began in 1975<ref>{{cite journal | vauthors = Bray F, Tyczynski JE, Parkin DM | title = Going up or coming down? The changing phases of the lung cancer epidemic from 1967 to 1999 in the 15 European Union countries | journal = European Journal of Cancer | volume = 40 | issue = 1 | pages = 96–125 | date = January 2004 | pmid = 14687795 | doi = 10.1016/j.ejca.2003.08.005 }}</ref> but by 1991 had not manifested in a decrease in lung cancer–related mortalities amongst women.<ref name="isbn0-521-78719-X">{{Cite book|vauthors=Jones M, Fosbery R, Taylor D | title = Biology 1 | chapter = Answers to self-assessment questions | page = 250| publisher = Cambridge Advanced Sciences | isbn = 978-0-521-78719-2|year=2000}}</ref>

Smoke contains several carcinogenic [[pyrolysis|pyrolytic]] products that bind to [[DNA]] and cause [[Mutation|genetic mutation]]s. Particularly potent carcinogens are [[polycyclic aromatic hydrocarbon]]s (PAH), which are [[Toxication|toxicated]] to [[mutagen]]ic [[epoxide]]s. The first PAH to be identified as a carcinogen in tobacco smoke was [[benzopyrene]], which has been shown to toxicate into an epoxide that irreversibly attaches to a cell's nuclear DNA, which may either kill the cell or cause a genetic mutation. If the mutation inhibits [[programmed cell death]], the cell can survive to become a cancer cell. Similarly, [[acrolein]], which is abundant in tobacco smoke, also irreversibly binds to DNA, causes mutations and thus also cancer. However, it needs no activation to become carcinogenic.<ref name="Feng">{{cite journal | vauthors = Feng Z, Hu W, Hu Y, Tang MS | title = Acrolein is a major cigarette-related lung cancer agent: Preferential binding at p53 mutational hotspots and inhibition of DNA repair | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 103 | issue = 42 | pages = 15404–9 | date = October 2006 | pmid = 17030796 | pmc = 1592536 | doi = 10.1073/pnas.0607031103 | bibcode = 2006PNAS..10315404F | doi-access = free }}</ref>

There are over 19 known carcinogens in cigarette smoke.<ref>{{cite web| vauthors = Koop CE | author-link1 = C. Everett Koop |title=Smoking and smokeless tobacco |url= http://www.drkoop.com/ency/93/002032.html |access-date=July 15, 2006|url-status=dead|archive-url=https://web.archive.org/web/20060723013314/http://www.drkoop.com/ency/93/002032.html|archive-date=July 23, 2006}}</ref> The following are some of the most potent carcinogens:

* '''[[Polycyclic aromatic hydrocarbon]]s''' are [[Tar (tobacco residue)|tar]] components produced by [[pyrolysis]] in smoldering organic matter and emitted into smoke. Several of these PAH's are already toxic in their normal form, however, many of then can become more toxic to the liver. Due to the [[hydrophobic]] nature of PAH's they do not dissolve in water and are hard to expel from the body. In order to make the PAH more soluble in water, the liver creates an enzyme called [[Cytochrome P450]] which adds an additional [[oxygen]] to the PAH, turning it into a [[mutagen]]ic [[epoxide]]s, which is more soluble, but also more reactive.<ref name="Hecht1999"/> The first PAH to be identified as a carcinogen in tobacco smoke was '''[[benzopyrene]]''', which been shown to toxicate into a diol epoxide and then permanently attach to nuclear DNA, which may either kill the cell or cause a [[Mutation|genetic mutation]]. The DNA contains the information on how the cell function; in practice, it contains the recipes for protein synthesis. If the mutation inhibits [[programmed cell death]], the cell can survive to become a cancer, a cell that does not function like a normal cell. The carcinogenicity is radiomimetic, i.e. similar to that produced by ionizing nuclear radiation. Tobacco manufacturers have experimented with combustion less [[vaporizer (cannabis)|vaporizer]] technology to allow cigarettes to be consumed without the formation of carcinogenic benzopyrenes.<ref>{{cite web|title=DNA interaction with Benzopyrene|work=DNA|url=http://www.mybiology.com/chime/dna_benzopyrene/dna_benzopyrene_text.htm|access-date=March 5, 2005|archive-url =https://web.archive.org/web/20041223072159/http://www.mybiology.com/chime/dna_benzopyrene/dna_benzopyrene_text.htm <!-- Bot retrieved archive --> |archive-date = December 23, 2004}}</ref> Although such products have become increasingly popular, they still represent a very small fraction of the market, and no conclusive evidence has shown to prove or disprove the positive health claims.{{Citation needed|date=April 2012}}
* '''[[Acrolein]]''' is a pyrolysis product that is abundant in cigarette smoke. It gives smoke an acrid smell and an irritating, tear causing effect and is a major contributor to its carcinogenicity. Like PAH metabolites, acrolein is also an electrophilic [[alkylation|alkylating agent]] and permanently binds to the DNA base [[guanine]], by a [[Nucleophilic conjugate addition|conjugate addition]] followed by cyclization into a [[hemiaminal]]. The acrolein-guanine adduct induces mutations during DNA copying and thus causes cancers in a manner similar to PAHs. However, acrolein is 1000 times more abundant than PAHs in cigarette smoke and is able to react as is, without metabolic activation. Acrolein has been shown to be a [[mutagen]] and [[carcinogen]] in human cells. The carcinogenicity of acrolein has been difficult to study by [[Animal testing|animal experimentation]], because it has such a toxicity that it tends to kill the animals before they develop cancer.<ref name="Feng"/> Generally, compounds able to react by [[Nucleophilic conjugate addition|conjugate addition]] as [[electrophile]]s (so-called ''Michael acceptors'' after [[Michael reaction]]) are toxic and carcinogenic, because they can permanently alkylate DNA, similarly to [[Sulfur mustard|mustard gas]] or [[aflatoxin]]. Acrolein is only one of them present in cigarette smoke; for example, [[crotonaldehyde]] has been found in cigarette smoke.<ref name="Kataoka">{{cite journal |vauthors=Kataoka H, Sumida A, Makita M | title = Determination of aliphatic and aromatic aldehydes in cigarette smoke by gas chromatography with flame photometric detection | year = 1997 | journal = Chromatographia | volume = 44 |issue = 9–10 | pages = 491–6 | doi =10.1007/BF02466742 | s2cid = 97329744 }}</ref> Michael acceptors also contribute to the chronic inflammation present in tobacco disease.<ref name="Facchinetti" />
* '''[[Nitrosamine]]s''' are a group of carcinogenic compounds found in cigarette smoke but not in uncured tobacco leaves. Nitrosamines form on flue-cured tobacco leaves during the curing process through a [[chemical reaction]] between nicotine and other compounds contained in the uncured leaf and various [[Nitrogen oxide|oxides of nitrogen]] found in all combustion gasses. Switching to Indirect fire curing has been shown to reduce nitrosamine levels to less than 0.1 parts per million.<ref name="urlwww.caes.uga.edu">{{cite web | url =http://www.caes.uga.edu/departments/bae/extension/pubs/documents/RetrofittingTobaccoCuringBarns.pdf | title = Retrofitting Tobacco Curing Barns |vauthors=Sumner PE, Moore JM, Boyette MD | work =  Extension Engineering Publications | publisher = The University of Georgia College of Agricultural and Environmental Sciences  | access-date = 2012-05-06}}</ref><ref>{{cite web | author = NOVA | url = https://www.pbs.org/wgbh/nova/cigarette/history2.html | title = Search for a Safer Cigarette | website = [[PBS]] | author-link = Nova (American TV series) }}</ref>

Sidestream tobacco smoke, or exhaled mainstream smoke, is particularly harmful. Because exhaled smoke exists at lower temperatures than inhaled smoke, chemical compounds undergo changes which can cause them to become more dangerous. As well, smoke undergoes changes as it ages, which causes the transformation of the compound NO into the more toxic NO<sub>2</sub>. Further, volatilization causes smoke particles to become smaller, and thus more easily embedded deep into the lung of anyone who later breathes the air.<ref name="isbn1-56670-402-2">{{cite book | vauthors = Godish T | title = Indoor environmental quality | publisher = Lewis Publishers | location = Chelsea, Michigan | year = 2001  | pages = 77–9| isbn = 978-1-56670-402-1 | url = https://books.google.com/books?id=cGlTz8d7j_sC&pg=PA77 }}</ref>

=== Radioactive carcinogens ===
In addition to chemical, nonradioactive carcinogens, tobacco and tobacco smoke contain small amounts of [[lead-210]] (<sup>210</sup>Pb) and [[polonium-210]] (<sup>210</sup>Po), both of which are radioactive carcinogens. The presence of polonium-210 in mainstream cigarette smoke has been experimentally measured at levels of 0.0263–0.036 [[Curie (unit)|pCi]] (0.97–1.33 [[Becquerel|mBq]]),<ref>{{cite web | url=http://www.rebek.co.uk/smoking-health-and-personality | title=Smoking, Health And Personality | date=May 13, 2015 | publisher=REBEK | access-date=2015-05-13 | archive-url=https://web.archive.org/web/20150518082025/http://www.rebek.co.uk/smoking-health-and-personality | archive-date=2015-05-18 | url-status=dead }}</ref><ref>{{cite web|url=http://chppm-www.apgea.army.mil/documents/TG/TECHGUID/TG238.pdf |author=[[U.S. Army]] Center for Health Promotion and Preventive Medicine |title=Radiological Sources of Potential Exposure and/or Contamination |url-status=dead |archive-url=https://web.archive.org/web/20061212063045/http://chppm-www.apgea.army.mil/documents/TG/TECHGUID/TG238.pdf |archive-date=December 12, 2006 }}</ref> which is equivalent to about 0.1 pCi per milligram of smoke (4 mBq/mg); or about 0.81 pCi of lead-210 per gram of dry condensed smoke (30 Bq/kg).

Research by [[National Center for Atmospheric Research|NCAR]] [[radiochemistry|radiochemist]] [[Edward Martell|Ed Martell]] suggested that radioactive compounds in cigarette smoke are deposited in "hot spots" where [[Bronchus|bronchial tubes]] branch, that tar from cigarette smoke is resistant to dissolving in lung fluid and that radioactive compounds have a great deal of time to undergo [[radioactive decay]] before being cleared by natural processes. Indoors, these radioactive compounds can linger in second-hand smoke, and greater exposure would occur when these radioactive compounds are inhaled during normal breathing, which is deeper and longer than when inhaling cigarettes. Damage to the protective [[epithelium|epithelial]] tissue from smoking only increases the prolonged retention of insoluble polonium-210 compounds produced from burning tobacco. Martell estimated that a carcinogenic radiation dose of 80–100 rads is delivered to the lung tissue of most smokers who die of lung cancer.<ref name="pmid6572389">{{cite journal | vauthors = Martell EA | title = alpha-Radiation dose at bronchial bifurcations of smokers from indoor exposure to radon progeny | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 80 | issue = 5 | pages = 1285–9 | date = March 1983 | pmid = 6572389 | pmc = 393580 | doi = 10.1073/pnas.80.5.1285 | bibcode = 1983PNAS...80.1285M | doi-access = free }}</ref><ref name=Muggli2008>{{cite journal | vauthors = Muggli ME, Ebbert JO, Robertson C, Hurt RD | title = Waking a sleeping giant: the tobacco industry's response to the polonium-210 issue | journal = American Journal of Public Health | volume = 98 | issue = 9 | pages = 1643–50 | date = September 2008 | pmid = 18633078 | pmc = 2509609 | doi = 10.2105/AJPH.2007.130963 }}</ref><ref name=Rego2009>{{cite journal | vauthors = Rego B | title = The Polonium brief: a hidden history of cancer, radiation, and the tobacco industry | journal = Isis; an International Review Devoted to the History of Science and Its Cultural Influences | volume = 100 | issue = 3 | pages = 453–84 | date = September 2009 | pmid = 19960838 | doi = 10.1086/644613 | s2cid = 26001557 | url = http://www.briannarego.org/RegoIsis2009.pdf | access-date = 2014-07-20 | archive-url = https://web.archive.org/web/20160304103812/http://www.briannarego.org/RegoIsis2009.pdf | archive-date = 2016-03-04 | url-status = dead }}</ref>

Smoking an average of 1.5 packs per day gives a radiation dose of 60-160 [[mSv]]/year,<ref name="urlF. Typical Sources of Radiation Exposure">{{cite web|url=http://www.ors.od.nih.gov/sr/drs/training/GRS/Pages/sectionf.aspx|title=F. Typical Sources of Radiation Exposure|publisher=United States National Institutes of Health|archive-url=https://web.archive.org/web/20130613131654/http://www.ors.od.nih.gov/sr/drs/training/GRS/Pages/sectionf.aspx|archive-date=2013-06-13|author=Office of Research Services, Division of Radiation Safety|access-date=2012-05-06}}</ref><ref name="urlRadiation Risk for Xray and CT exams - dosage chart">{{cite web|url=http://www.aradnj.com/radiation2.html |title=Radiation Risk for Xray and CT exams – |publisher=Associated Radiologists |work=dosage chart |access-date=2012-05-06 |url-status=dead |archive-url=https://web.archive.org/web/20120426011721/http://www.aradnj.com/radiation2.html |archive-date=April 26, 2012 }}</ref> compared with living near a nuclear power station (0.0001 mSv/year)<ref name=epa>{{cite web | url =http://www.epa.gov/rpdweb00/docs/402-k-07-006.pdf | title = Radiation Risks and Realities | publisher = United States Environmental Protection Agency | date = 2014-07-16 }}</ref><ref name=pbs>{{cite web | url =https://www.pbs.org/wgbh/pages/frontline/shows/reaction/interact/facts.html|title=Everyday exposures to radiation | work = Front Line | publisher = Public Broadcasting System }}</ref> or the 3.0 mSv/year average dose for Americans.<ref name="pbs"/><ref name=bbc>{{cite news |url=https://www.bbc.co.uk/news/health-12722435 | title = Radiation fears after Japan blast | publisher = [[BBC]] | date=2011-07-21}}</ref> Some of the mineral apatite in Florida used to produce phosphate for U.S. tobacco crops contains uranium, radium, lead-210 and polonium-210 and radon.<ref>{{cite news| url=https://www.nytimes.com/2006/12/01/opinion/01proctor.html | work = The New York Times | vauthors = Proctor RN | title = Puffing on Polonium | date=2006-12-01}}</ref><ref name="urlTobacco Smoke | Radiation Protection | US EPA">{{cite web | url =http://www.epa.gov/radiation/sources/tobacco.html#material_cigarette | title = Tobacco Smoke &#124; Radiation Protection |publisher = United States Environmental Protection Agency | access-date = 2012-05-06 }}</ref> The radioactive smoke from tobacco fertilized this way is deposited in lungs and releases radiation even if a smoker quits the habit. The combination of carcinogenic tar and radiation in a sensitive organ such as lungs increases the risk of cancer.{{citation needed|date=October 2016}}

In contrast, a 1999 review of tobacco smoke carcinogens published in the ''[[Journal of the National Cancer Institute]]'' states that "levels of polonium-210 in tobacco smoke are not believed to be great enough to significantly impact lung cancer in smokers."<ref name=Hecht1999>{{cite journal | vauthors = Hecht SS | title = Tobacco smoke carcinogens and lung cancer | journal = Journal of the National Cancer Institute | volume = 91 | issue = 14 | pages = 1194–210 | date = July 1999 | pmid = 10413421 | doi = 10.1093/jnci/91.14.1194 | doi-access = free }}</ref> In 2011 Hecht has also stated that the "levels of <sup>210</sup>Po in cigarette smoke are probably too low to be involved in lung cancer induction".<ref name=Hecht2011>{{cite book| vauthors = Hecht SS | veditors = Penning TM |title=Chemical Carcinogenesis |date=2011 |publisher=Springer |location=Totowa, NJ|isbn=9781617379949|page=67|chapter-url=https://books.google.com/books?id=N4tU04rn6HgC&q=210po|chapter=Tobacco smoke carcinogens and lung cancer}}</ref>

=== Oxidation and inflammation ===
[[Radical (chemistry)|Free radical]]s and [[Oxidizing agent|pro-oxidants]] in cigarettes damage blood vessels and oxidize [[Low-density lipoprotein|LDL cholesterol]].<ref name="pmid24554606">{{cite journal | vauthors=Messner B, Bernhard D | title=Smoking and cardiovascular disease: mechanisms of endothelial dysfunction and early atherogenesis | journal= [[Arteriosclerosis, Thrombosis, and Vascular Biology]] | volume=34 |issue=3 | pages=509–515| year=2014 | doi=10.1161/ATVBAHA.113.300156 | pmid = 24554606 | doi-access=free }}</ref> Only oxidized LDL cholesterol is taken-up by [[macrophage]]s, which become [[foam cell]]s, leading to [[Atheroma|atherosclerotic plaques]].<ref name="pmid24554606" /> Cigarette smoke increases [[proinflammatory cytokine]]s in the bloodstream, causing [[atherosclerosis]].<ref name="pmid24554606" /> The pro-oxidative state also leads to [[endothelial dysfunction]],<ref name="pmid24554606" /> which is another important cause of atherosclerosis.<ref name="pmid12588755">{{cite journal | vauthors=Bonetti PO, Lerman LO, Lerman A | title=Endothelial dysfunction: a marker of atherosclerotic risk | journal= [[Arteriosclerosis, Thrombosis, and Vascular Biology]] | volume=23 |issue=2 | pages=168–175 | year=2003 | pmid = 12588755 | doi=10.1161/01.ATV.0000051384.43104.FC | s2cid=34213675 }}</ref>

=== Nicotine ===
{{Main|Nicotine}}
[[File:Nicotine.svg|thumb|Nicotine molecule]]

[[Nicotine]], which is contained in cigarettes and other smoked tobacco products, is a [[stimulant]] and is one of the main factors leading to continued tobacco smoking. Nicotine is a highly addictive psychoactive chemical. When tobacco is smoked, most of the nicotine is [[Pyrolysis|pyrolyzed]]; a dose sufficient to cause mild somatic dependency and mild to strong psychological dependency remains. The amount of nicotine absorbed by the body from smoking depends on many factors, including the type of tobacco, whether the smoke is inhaled, and whether a filter is used. There is also a formation of [[harmane]] (a [[Monoamine oxidase inhibitor|MAO inhibitor]]) from the [[acetaldehyde]] in cigarette smoke, which seems to play an important role in nicotine addiction<ref>{{cite journal | vauthors = Talhout R, Opperhuizen A, van Amsterdam JG | title = Role of acetaldehyde in tobacco smoke addiction | journal = European Neuropsychopharmacology | volume = 17 | issue = 10 | pages = 627–36 | date = October 2007 | pmid = 17382522 | doi = 10.1016/j.euroneuro.2007.02.013 | s2cid = 25866206 }}</ref> probably by facilitating dopamine release in the nucleus accumbens in response to nicotine stimuli. According to studies by Henningfield and Benowitz, nicotine is more addictive than [[Cannabis (drug)|cannabis]], [[caffeine]], [[ethanol|alcohol]], [[cocaine]], and [[heroin]] when considering both somatic and psychological dependence. However, due to the stronger withdrawal effects of alcohol, cocaine and heroin, nicotine may have a lower potential for somatic dependence than these substances.<ref name="urlRelative Addictiveness of Drugs (NYT 8/2/94)">{{cite web | url = http://www.tfy.drugsense.org/tfy/addictvn.htm | title = Relative Addictiveness of Drugs | vauthors = Hilts PJ | date = 1994-08-02 | work = [[The New York Times]]  | access-date = 2012-05-06 }}</ref><ref name="urlb.rox.com">{{cite web | url = http://b.rox.com/gizmos/henningfield-benowitz/combo.swf | title = The Henningfield-Benowitz substance comparison charts | access-date = 2012-05-06 }}</ref> About half of Canadians who currently smoke have tried to quit.<ref name="urlHome | Alberta Health Services">{{cite web| url =http://www.ecigator.net/blog/truth-tobacco-addiction| archive-url =https://web.archive.org/web/20140225062752/http://www.ecigator.net/blog/truth-tobacco-addiction| url-status =dead| archive-date =2014-02-25| title =AADAC{{!}}Truth About Tobacco – Addiction| publisher =Alberta Health Services}}</ref> [[McGill University]] health professor Jennifer O'Loughlin stated that nicotine addiction can occur as soon as five months after the start of smoking.<ref name="pmid16880445">{{cite journal | vauthors = Gervais A, O'Loughlin J, Meshefedjian G, Bancej C, Tremblay M | title = Milestones in the natural course of onset of cigarette use among adolescents | journal = CMAJ | volume = 175 | issue = 3 | pages = 255–61 | date = August 2006 | pmid = 16880445 | pmc = 1513423 | doi = 10.1503/cmaj.051235 }}</ref>

Ingesting a compound by smoking is one of the most rapid and efficient methods of introducing it into the bloodstream, second only to injection, which allows for the rapid feedback which supports the smokers' ability to [[Titration|titrate]] their dosage. On average it takes about ten seconds for the substance to reach the brain. As a result of the efficiency of this delivery system, many smokers feel as though they are unable to cease. Of those who attempt cessation and last three months without succumbing to nicotine, most are able to remain smoke-free for the rest of their lives.<ref name=NCI_quit>{{cite web | url =http://www.cancer.gov/cancertopics/factsheet/Tobacco/cessation | title = Harms of Smoking and Health Benefits of Quitting  | author = National Cancer Institute | work = Fact Sheet | publisher = United States National Institutes of Health | access-date = 2012-05-06 }}</ref>{{Failed verification|date=March 2016}} There exists a possibility of depression in some who attempt cessation, as with other psychoactive substances. Depression is also common in teenage smokers; teens who smoke are four times as likely to develop depressive symptoms as their nonsmoking peers.<ref name="urlSmoking increases teen depression">{{cite web | url = http://www.apa.org/monitor/dec00/smoking.html | title = Smoking increases teen depression | vauthors = Smith D | year = 2000 | work = Monitor on Psychology | publisher = American Psychological Association  |access-date = 2012-05-06 }}</ref>

Although nicotine does play a role in acute episodes of some diseases (including [[stroke]], [[Erectile dysfunction|impotence]], and [[heart disease]]) by its stimulation of [[Epinephrine|adrenaline]] release, which raises blood pressure,<ref name="Narkiewicz_2005">{{cite journal | vauthors = Narkiewicz K, Kjeldsen SE, Hedner T | title = Is smoking a causative factor of hypertension? | journal = Blood Pressure | volume = 14 | issue = 2 | pages = 69–71 | year = 2005 | pmid = 16036482 | doi = 10.1080/08037050510034202 | s2cid = 40476025 }}</ref> heart and respiration rate, and [[free fatty acids]], the most serious longer term effects are more the result of the products of the smouldering combustion process. This has led to the development of various nicotine delivery systems, such as the [[nicotine patch]] or [[nicotine gum]], that can satisfy the addictive craving by delivering nicotine without the harmful combustion by-products. This can help the heavily dependent smoker to quit gradually while discontinuing further damage to health.{{citation needed|date=October 2016}}

Recent evidence has shown that smoking tobacco increases the release of [[dopamine]] in the brain, specifically in the mesolimbic pathway, the same neuro-reward circuit activated by addictive substances such as heroin and cocaine. This suggests nicotine use has a pleasurable effect that triggers positive reinforcement.<ref name="urlTobacco Addiction | Mind Over Matter | National Institute on Drug Abuse">{{cite web | url = http://www.drugabuse.gov/publications/mind-over-matter/tobacco-addiction | title = Mind Over Matter: Tobacco Addiction | author = National Institute on Drug Abuse | publisher = United States National Institutes of Health | access-date = 2012-05-06 | url-status = dead | archive-url = https://web.archive.org/web/20120505231933/http://www.drugabuse.gov/publications/mind-over-matter/tobacco-addiction | archive-date = 2012-05-05 }}</ref> One study found that smokers exhibit better reaction-time and memory performance compared to non-smokers, which is consistent with increased activation of dopamine receptors.<ref name="pmid9551774">{{cite journal | vauthors = Parkin C, Fairweather DB, Shamsi Z, Stanley N, Hindmarch I | title = The effects of cigarette smoking on overnight performance | journal = Psychopharmacology | volume = 136 | issue = 2 | pages = 172–8 | date = March 1998 | pmid = 9551774 | doi = 10.1007/s002130050553 | s2cid = 22962937 }}</ref> Neurologically, [[animal testing on rodents|rodent studies]] have found that nicotine self-administration causes lowering of reward thresholds—a finding opposite that of most other addictive substances (e.g. cocaine and heroin).

The carcinogenity of tobacco smoke is not explained by nicotine per se, which is not carcinogenic or mutagenic, although it is a metabolic precursor for several compounds which are.{{citation needed|date=September 2012}} In addition, it inhibits [[apoptosis]], therefore accelerating existing cancers.<ref>{{cite journal | vauthors = Maneckjee R, Minna JD | title = Opioids induce while nicotine suppresses apoptosis in human lung cancer cells | journal = Cell Growth & Differentiation | volume = 5 | issue = 10 | pages = 1033–40 | date = October 1994 | pmid = 7848904 }}</ref> Also, [[NNK]], a nicotine derivative converted from nicotine, can be carcinogenic.

It is worth noting that nicotine, although frequently implicated in producing [[tobacco]] addiction, is not significantly addictive when administered alone.<ref name="pmid16177026">{{cite journal | vauthors = Guillem K, Vouillac C, Azar MR, Parsons LH, Koob GF, Cador M, Stinus L | title = Monoamine oxidase inhibition dramatically increases the motivation to self-administer nicotine in rats | journal = The Journal of Neuroscience | volume = 25 | issue = 38 | pages = 8593–600 | date = September 2005 | pmid = 16177026 | pmc = 6725504 | doi = 10.1523/JNEUROSCI.2139-05.2005 }}</ref>{{primary source inline|date=December 2018}} The addictive potential manifests itself after co-administration of an [[Monoamine oxidase inhibitor|MAOI]], which specifically causes [[sensitization]] of the [[Human musculoskeletal system|locomotor]] response in rats, a measure of addictive potential.<ref name="pmid14592678">{{cite journal | vauthors = Villégier AS, Blanc G, Glowinski J, Tassin JP | title = Transient behavioral sensitization to nicotine becomes long-lasting with monoamine oxidases inhibitors | journal = Pharmacology Biochemistry and Behavior | volume = 76 | issue = 2 | pages = 267–74 | date = September 2003 | pmid = 14592678 | doi = 10.1016/S0091-3057(03)00223-5 | s2cid = 30370768 }}</ref>

== Forms of exposure ==

=== Second-hand smoke ===
{{Main|Passive smoking}}
[[File:Smoking.jpg|thumb|Posted sign to avoid passive smoking in [[York University]], [[Toronto]], [[Ontario]], [[Canada]]]]
Second-hand smoke is a mixture of smoke from the burning end of a cigarette, pipe or cigar, and the smoke exhaled from the lungs of smokers. It is involuntarily inhaled, lingers in the air hours after cigarettes have been extinguished, and may cause a wide range of adverse health effects, including [[cancer]], [[respiratory tract infection|respiratory infections]], and [[asthma]].<ref name="ALASecondhandSmokeFactSheet">{{cite web|url=http://www.lung.org/stop-smoking/about-smoking/health-effects/secondhand-smoke.html|title=Secondhand Smoke|date=June 2007|publisher=American Lung Association|access-date=2012-05-06}}<!--http://www.lungusa.org/site/pp.asp?c=dvLUK9O0E&b=35422#one --></ref>

Studies have shown that exposure to second-hand smoke causes harmful effects on the [[cardiovascular system]] and is associated with prevalent [[heart failure]] among non-smokers.<ref name="Nicotine Tob. Res.">{{cite journal | vauthors = Skipina TM, Upadhya B, Soliman EZ | title = Secondhand Smoke Exposure is Associated with Prevalent Heart Failure: Longitudinal Examination of the National Health and Nutrition Examination Survey | journal = [[Nicotine & Tobacco Research]] | volume = 23 | issue = 9 | pages = 1512–1517 | date = July 2021 | pmid = 34213549 | doi = 10.1093/ntr/ntab047 | publisher = [[Oxford University Press]] on behalf of the [[Society for Research on Nicotine and Tobacco]] | lccn = 00244999  | s2cid = 235707832 | veditors = Munafò M | editor-link = Marcus Munafo | eissn = 1469-994X  }}</ref> Non-smokers who are exposed to second-hand smoke at home or work are thought, due to a wide variety of statistical studies, to increase their heart disease risk by 25–30% and their lung cancer risk by 20–30%. Second-hand smoke has been estimated to cause 38,000 deaths per year, of which 3,400 are deaths from [[lung cancer]] in non-smokers.<ref>{{cite web|url=http://www.tobaccofreefloridanewsroom.com/?cat=6|title="Tobacco-Free Florida", ''Centers for Disease Control & Prevention Fact Sheets''|access-date=8 September 2014}}</ref>

The current US Surgeon General's Report concludes that there is no established risk-free level of exposure to [[second-hand smoke]]. Short exposures to second-hand smoke are believed to cause blood [[platelets]] to become stickier, damage the lining of [[blood vessel]]s, decrease coronary flow velocity reserves, and reduce heart rate variability, potentially increasing the mortality of [[Myocardial infarction|heart attack]]s.<ref>{{Cite journal |last1=Woo |first1=Mary A. |last2=Stevenson |first2=William G. |last3=Moser |first3=Debra K. |last4=Trelease |first4=Robert B. |last5=Harper |first5=Ronald M. |date=1992-03-01 |title=Patterns of beat-to-beat heart rate variability in advanced heart failure |url=https://dx.doi.org/10.1016/0002-8703%2892%2990510-3 |journal=American Heart Journal |language=en |volume=123 |issue=3 |pages=704–710 |doi=10.1016/0002-8703(92)90510-3 |pmid=1539521 |issn=0002-8703}}</ref> New research indicates that private research conducted by cigarette company [[Philip Morris International|Philip Morris]] in the 1980s showed that second-hand smoke was toxic, yet the company suppressed the finding during the next two decades.<ref name="ALASecondhandSmokeFactSheet" />

=== Chewing tobacco ===
[[Chewing tobacco]] has been known to cause cancer, particularly of the mouth and throat.<ref name="IARC">{{cite journal | author = IARC Working Group on the Evaluation of Carcinogenic Risks to Humans | title = Smokeless tobacco and some tobacco-specific N-nitrosamines | journal = IARC Monographs on the Evaluation of Carcinogenic Risks to Humans | volume = 89 | pages = 1–592 | year = 2007 | pmid = 18335640 | pmc = 4781254 | url = http://monographs.iarc.fr/ENG/Monographs/vol89/mono89-6E.pdf }}</ref> According to the [[International Agency for Research on Cancer]], "Some health scientists have suggested that smokeless tobacco should be used in smoking cessation programmes and have made implicit or explicit claims that its use would partly reduce the exposure of smokers to carcinogens and the risk for cancer. These claims, however, are not supported by the available evidence."<ref name="IARC"/> Oral and spit tobacco increase the risk for [[leukoplakia]], a precursor to [[oral cancer]].<ref name="urlwww.cancer.org">{{cite web | url = http://www.cancer.org/Cancer/GestationalTrophoblasticDisease/DetailedGuide/gestational-trophoblastic-disease-what-is-cancer | title = What is cancer? | date = 2011-04-11 | work = Detailed Guide | publisher = American Cancer Society }}</ref>

=== Cigars ===
Like other forms of smoking, [[cigar]] smoking poses a significant health risk depending on dosage: risks are greater for those who inhale more when they smoke, smoke more cigars, or smoke them longer.<ref name="Symm_2005"/> The risk of dying from any cause is significantly greater for cigar smokers, with the risk particularly higher for smokers less than 65 years old, and with risk for moderate and deep inhalers reaching levels similar to cigarette smokers.<ref name="pmid18569755">{{cite journal | vauthors = Dollar KM, Mix JM, Kozlowski LT | title = Little cigars, big cigars: omissions and commissions of harm and harm reduction information on the Internet | journal = Nicotine & Tobacco Research | volume = 10 | issue = 5 | pages = 819–26 | date = May 2008 | pmid = 18569755 | doi = 10.1080/14622200802027214 | citeseerx = 10.1.1.1009.3126 }}</ref> The increased risk for those smoking 1–2 cigars per day is too small to be statistically significant,<ref name=Shanks>{{cite book |vauthors=Shanks TG, Burns DM | chapter = Disease Consequences of Cigar Smoking | chapter-url = http://www.cancercontrol.cancer.gov/tcrb/monographs/9/m9_4.PDF |veditors=Shopland DR, Burns DM, Hoffmann D, Cummings KM, Amacher RH |date=February 1988 | title = Cigars: Health Effects and Trends | publisher = National Cancer Institute | series = Smoking and Tobacco Control Monograph No. 9 | pages = 105–60 }}</ref> and the health risks of the 3/4 of cigar smokers who smoke less than daily are not known<ref>{{cite web |url=http://www.cancer.gov/cancertopics/factsheet/Tobacco/cigars |access-date=2008-10-21 |title= Questions and answers about cigar smoking and cancer |date=2000-03-07 |publisher= National Cancer Institute}}</ref> and are hard to measure.<!-- <ref name=Burns/> --> Although it has been claimed that people who smoke few cigars have no increased risk, a more accurate statement is that their risks are proportionate to their exposure.<ref name=Burns>{{cite book | title = Cigars: Health Effects and Trends |veditors=Shopland DR, Burns DM, Hoffmann D, Cummings KM, Amacher RH | vauthors = Burns DM | chapter = Cigar smoking: overview and current state of the science | chapter-url = http://cancercontrol.cancer.gov/tcrb/monographs/9/m9_1.PDF | publisher = National Cancer Institute | series = Smoking and Tobacco Control Monograph No. 9 | year = 1998 | pages = 1–20 }}</ref> Health risks are similar to [[cigarette]] smoking in [[nicotine]] addiction, [[Periodontology|periodontal]] health, tooth loss, and many types of cancer, including cancers of the [[Oral cancer|mouth]], throat, and [[esophageal cancer|esophagus]].<ref name="Chang_2015">{{cite journal | vauthors = Chang CM, Corey CG, Rostron BL, Apelberg BJ | title = Systematic review of cigar smoking and all cause and smoking related mortality | journal = BMC Public Health | volume = 15 | issue = | pages = 390 | date = April 2015 | pmid = 25907101 | pmc = 4408600 | doi = 10.1186/s12889-015-1617-5 }}</ref><ref name="Shapiro_2000">{{cite journal | vauthors = Shapiro JA, Jacobs EJ, Thun MJ | title = Cigar smoking in men and risk of death from tobacco-related cancers | journal = Journal of the National Cancer Institute | volume = 92 | issue = 4 | pages = 333–7 | date = February 2000 | pmid = 10675383 | doi = 10.1093/jnci/92.4.333 | publisher = [[Oxford University Press]] | eissn = 1460-2105 | s2cid = 7772405 | veditors = Ganz PA | editor-link = Patricia A. Ganz | doi-access = free | department = Primary }}</ref>{{Unreliable medical source|date=August 2021}} Cigar smoking also can cause cancers of the [[Lung cancer|lung]], and [[Laryngeal cancer|larynx]], where the increased risk is less than that of cigarettes. Many of these cancers have extremely low cure rates. Cigar smoking also increases the risk of lung and heart diseases such as [[chronic obstructive pulmonary disease]] (COPD).<ref name="Symm_2005"/><ref name="Rodu_2021">{{cite journal | vauthors = Rodu B, Plurphanswat N | title = Mortality among male cigar and cigarette smokers in the USA | journal = Harm Reduction Journal | volume = 18 | issue = 1 | pages = 7 | date = January 2021 | pmid = 33413424 | pmc = 7789747 | doi = 10.1186/s12954-020-00446-4 | url = https://harmreductionjournal.biomedcentral.com/track/pdf/10.1186/s12954-020-00446-4.pdf | publisher = [[BioMed Central]] | s2cid = 230800394 | doi-access = free | lccn = 2004243422 | department = Primary }}</ref>{{Unreliable medical source|date=August 2021}}<ref name="Nonnemaker_2014">{{cite journal | vauthors = Nonnemaker J, Rostron B, Hall P, MacMonegle A, Apelberg B | title = Mortality and economic costs from regular cigar use in the United States, 2010 | journal = American Journal of Public Health | volume = 104 | issue = 9 | pages = e86-91 | date = September 2014 | pmid = 25033140 | pmc = 4151956 | doi = 10.2105/AJPH.2014.301991 | publisher = [[American Public Health Association]] | s2cid = 207276270 | veditors = Morabia A | editor-link = Alfredo Morabia | eissn = 1541-0048 | department = Primary }}</ref>{{Unreliable medical source|date=August 2021}}

=== Hookahs ===
[[File:Cigaretttes, vaping and hookah ban.jpg|thumb|A sign forbidding the use of cigarettes, e-cigarettes and hookah in [[Tbilisi]], [[Georgia (country)|Georgia]]]]
A common belief among users is that the smoke of a [[hookah]] (waterpipe, narghile) is significantly less dangerous than that from cigarettes.<ref>{{cite news |work=[[The Independent Florida Alligator]] |title=UF study finds more teens smoke hookah | vauthors = Misner J |date=November 18, 2009 |url= http://www.alligator.org/news/campus/article_744a0e26-d403-11de-b968-001cc4c03286.html }}</ref> The water moisture induced by the hookah makes the smoke less irritating and may give a false sense of security and reduce concerns about true health effects.<ref name="pmid15995011">{{cite journal | vauthors = Knishkowy B, Amitai Y | title = Water-pipe (narghile) smoking: an emerging health risk behavior | journal = Pediatrics | volume = 116 | issue = 1 | pages = e113–9 | date = July 2005 | pmid = 15995011 | doi = 10.1542/peds.2004-2173 | doi-access = free }}</ref> Doctors at institutions including the [[Mayo Clinic]] have stated that use of hookah can be as detrimental to a person's health as smoking cigarettes,<ref name="mayoclinic.com">{{cite web | vauthors = Hurt RD | date = 2010-02-20 | title = Hookah smoking: Is it safer than cigarettes? | publisher = Mayo Clinic | url = http://www.mayoclinic.com/health/hookah/AN01265}}</ref><ref>{{cite news |title=EGYPT: Water pipe smoking a significant TB risk |date=March 24, 2008 |publisher=[[The New Humanitarian|IRIN]] |url=http://www.irinnews.org/Report.aspx?ReportId=77426}}</ref> and a study by the World Health Organization also confirmed these findings.<ref>{{cite news |agency=Reuters |date=March 17, 2007 |title=Egyptians warned on pipe smoking |work=[[The Australian]]}}</ref>

Each hookah session typically lasts more than 40 minutes, and consists of 50 to 200 inhalations that each range from 0.15 to 0.50 liters of smoke.<ref name="Shihadeh_2004">{{cite journal | vauthors = Shihadeh A, Azar S, Antonios C, Haddad A | title = Towards a topographical model of narghile water-pipe café smoking: a pilot study in a high socioeconomic status neighborhood of Beirut, Lebanon | journal = Pharmacology Biochemistry and Behavior | volume = 79 | issue = 1 | pages = 75–82 | date = September 2004 | pmid = 15388286 | doi = 10.1016/j.pbb.2004.06.005 | s2cid = 29182130 }}</ref><ref name="pmid10639511">{{cite journal | vauthors = Djordjevic MV, Stellman SD, Zang E | title = Doses of nicotine and lung carcinogens delivered to cigarette smokers | journal = Journal of the National Cancer Institute | volume = 92 | issue = 2 | pages = 106–11 | date = January 2000 | pmid = 10639511 | doi = 10.1093/jnci/92.2.106 }}</ref> In an hour-long smoking session of hookah, users consume about 100 to 200 times the smoke of a single cigarette;<ref name="Shihadeh_2004"/><ref name="USA Today hookah">{{cite news |agency=Associated Press |url=https://www.usatoday.com/news/health/2007-05-29-WHO-hooka_N.htm |title=WHO warns the hookah may pose same risk as cigarettes |date=May 29, 2007 |work=[[USA Today]]}}</ref> A study in the ''[[Journal of Periodontology]]'' found that water pipe smokers were marginally more likely than regular smokers to show signs of gum disease, showing rates 5-fold higher than non-smokers rather than the 3.8-fold risk that regular smokers show.<ref>{{cite journal | vauthors = Natto SB | title = Tobacco smoking and periodontal health in a Saudi Arabian population | journal = Swedish Dental Journal. Supplement | issue = 176 | pages = 8–52, table of contents | date = 2005 | pmid = 16223098 }}</ref> According to ''[[USA Today]]'', people who smoked water pipes had five times the risk of lung cancer of non-smokers.<ref>{{cite news | url = https://www.usatoday.com/news/nation/2005-12-28-hookah-trend_x.htm | title = Hookah trend is puffing along | date = 2005-12-28 | work = USA Today | vauthors = Koch W | access-date = 2010-05-04}}</ref>{{better source needed|reason=We should link to the actual study, not the USA today article|date=July 2016}}

A study on hookah smoking and cancer in [[Pakistan]] was published in 2008. Its objective was "to find serum [[Carcinoembryonic antigen|CEA]] levels in ever/exclusive hookah smokers, i.e. those who smoked only hookah (no cigarettes, [[Beedi|bidi]]s, etc.), prepared between 1 and 4 times a day with a quantity of up to 120 g of a tobacco-molasses mixture each (i.e. the tobacco weight equivalent of up to 60 cigarettes of 1 g each) and consumed in 1 to 8 sessions". Carcinoembryonic antigen (CEA) is a marker found in several forms of cancer. Levels in exclusive hookah smokers were lower compared to cigarette smokers although the difference was not as statistically significant as that between a hookah smoker and a non-smoker. Also, the study concluded that heavy hookah smoking (2–4 daily preparations; 3–8 sessions a day; >2 hrs to ≤ 6 hours) substantially raises CEA levels.<ref name="pmid18501010">{{cite journal | vauthors = Sajid KM, Chaouachi K, Mahmood R | title = Hookah smoking and cancer: carcinoembryonic antigen (CEA) levels in exclusive/ever hookah smokers | journal = Harm Reduction Journal | volume = 5 | pages = 19 | date = May 2008 | pmid = 18501010 | pmc = 2438352 | doi = 10.1186/1477-7517-5-19 }}</ref> Hookah smokers were nearly 6 times more likely to develop lung cancer than healthy non-smokers in Kashmir.<ref name="pmid21545223">{{cite journal | vauthors = Koul PA, Hajni MR, Sheikh MA, Khan UH, Shah A, Khan Y, Ahangar AG, Tasleem RA | title = Hookah smoking and lung cancer in the Kashmir valley of the Indian subcontinent | journal = Asian Pacific Journal of Cancer Prevention | volume = 12 | issue = 2 | pages = 519–24 | year = 2011 | pmid = 21545223 }}</ref>

=== Dipping tobacco ===
Dipping tobacco, commonly referred to as [[snuff (tobacco)|snuff]], is also put in the mouth, but it is a flavored powder. it is placed between the cheek and gum. Dipping tobacco does not need to be chewed for the nicotine to be absorbed. First-time users of these products often become nauseated and dizzy. Long-term effects include bad breath, yellowed teeth, and an increased risk of oral cancer.{{citation needed|date=October 2016}}

Users of dipping tobacco are believed to face less risk of some cancers than are smokers, but are still at greater risk than people who do not use any tobacco products.<ref name="pmid18598931">{{cite journal | vauthors = Boffetta P, Hecht S, Gray N, Gupta P, Straif K | title = Smokeless tobacco and cancer | journal = The Lancet. Oncology | volume = 9 | issue = 7 | pages = 667–75 | date = July 2008 | pmid = 18598931 | doi = 10.1016/S1470-2045(08)70173-6 }}</ref> They also have an equal risk of other health problems directly linked to nicotine, such as increased rate of [[atherosclerosis]].{{Citation needed|date=May 2012}}

== Prevention ==

Education and counselling by physicians of children and adolescents have been found to be effective in decreasing tobacco use.<ref>{{cite journal | title = Summaries for patients. Primary care interventions to prevent tobacco use in children and adolescents: U.S. Preventive Services Task Force recommendation statement | journal = Annals of Internal Medicine | volume = 159 | issue = 8 | pages = I–36 | date = October 2013 | pmid = 23974179 | doi = 10.7326/0003-4819-159-8-201310150-00699 | s2cid = 28035258 }}</ref>

<gallery widths="300px" heights="200px">
File:Average-price-of-a-pack-of-cigarettes.png|Average price of a pack of 20 cigarettes, measured in international dollars in 2014.<ref>{{cite web |title=Average price of a pack of cigarettes |url=https://ourworldindata.org/grapher/average-price-of-a-pack-of-cigarettes |website=Our World in Data |access-date=5 March 2020}}</ref>
File:Taxes-as-share-of-cigarette-price.png|Taxes as a share of cigarette price, 2014<ref>{{cite web |title=Taxes as a share of cigarette price |url=https://ourworldindata.org/grapher/taxes-as-share-of-cigarette-price |website=Our World in Data |access-date=5 March 2020}}</ref>
File:Enforcement-of-bans-on-tobacco-advertising.png|Types of bans on tobacco advertising, 2014<ref>{{cite web |title=Enforcement of bans on tobacco advertising |url=https://ourworldindata.org/grapher/enforcement-of-bans-on-tobacco-advertising |website=Our World in Data |access-date=5 March 2020}}</ref>
File:Support-to-help-to-quit-tobacco-use.png|Support to help quit tobacco use, 2014<ref>{{cite web |title=Support to help quit tobacco use |url=https://ourworldindata.org/grapher/support-to-help-to-quit-tobacco-use |website=Our World in Data |access-date=5 March 2020}}</ref>
</gallery>

== Usage ==
{{Multiple image|direction=vertical|align=right|image1=Female Smoking by Country.png|image2=Male Smoking by Country.png|width=250|caption1=Percentage of females smoking any tobacco product|caption2=Percentage of males smoking any tobacco product. Note that there is a difference between the scales used for females and for males.<ref name="isbn92-4-159628-7"/>}}

Though tobacco may be consumed by either smoking or other smokeless methods such as chewing, the [[World Health Organization]] (WHO) only collects data on smoked tobacco.<ref name="WHOPrevalenceAdultsAge15">{{cite web | url =https://www.who.int/whosis/indicators/compendium/2008/2ptu/en/ | title = Prevalence of current tobacco use among adults aged=15 years (percentage) | access-date = 2009-01-02 | publisher = World Health Organization | url-status = dead | archive-url = https://web.archive.org/web/20081211143334/http://www.who.int/whosis/indicators/compendium/2008/2ptu/en/ | archive-date = 2008-12-11 }}</ref> Smoking has therefore been studied more extensively than any other form of tobacco consumption.<ref name="WHOMayoReport">{{cite web | url =https://www.who.int/tobacco/resources/publications/mayo/en/index.html | archive-url =https://web.archive.org/web/20040512172549/http://www.who.int/tobacco/resources/publications/mayo/en/index.html | url-status =dead | archive-date =May 12, 2004 | title = Mayo report on addressing the worldwide tobacco epidemic through effective, evidence-based treatment | access-date = 2009-01-02 | publisher = World Health Organization | page = 2}}</ref>

In 2000, smoking was practiced by 1.22 billion people, predicted to rise to 1.45 billion people in 2010 and 1.5 to 1.9 billion by 2025. If prevalence had decreased by 2% a year since 2000 this figure would have been 1.3 billion in 2010 and 2025.<ref name="HNPGuindonBoisclair13-16">{{Cite book |vauthors=Guindon GE, Boisclair D | title=Past, current and future trends in tobacco use | url =http://siteresources.worldbank.org/HEALTHNUTRITIONANDPOPULATION/Resources/281627-1095698140167/Guindon-PastCurrent-whole.pdf| access-date=2009-03-22 | year=2003 | publisher = The International Bank for Reconstruction and Development / The World Bank|location=Washington DC | pages=13–16 | isbn = 978-1-932126-66-2 }}</ref> Despite dropping by 0.4 percent from 2009 to 2010, the United States still reports an average of 17.9 percent usage.<ref name="urlwww.americashealthrankings.org"/>

As of 2002, about twenty percent of young teens (13–15) smoked worldwide, with 80,000 to 100,000 children taking up the addiction every day, roughly half of whom live in Asia. Half of those who begin smoking in [[Adolescence|adolescent]] years are projected to go on to smoke for 15 to 20 years.<ref name="WHO2002FactSheet">{{cite web| url =http://www.wpro.who.int/media_centre/fact_sheets/fs_20020528.htm| title =WHO/WPRO-Smoking Statistics| access-date =2009-01-01| date =2002-05-28| publisher =World Health Organization Regional Office for the Western Pacific| url-status =dead| archive-url =https://web.archive.org/web/20091108181404/http://www.wpro.who.int/media_centre/fact_sheets/fs_20020528.htm| archive-date =2009-11-08}}</ref>

Teens are more likely to use e-cigarettes than cigarettes. About 31% of teenagers who use e-cigs started smoking within six months, compared to 8% of non-smokers. Manufacturers do not have to report what is in e-cigs, and most teens either say e-cigs contain only flavoring, or that they do not know what they contain.<ref name="Teens and E-Cigarettes">{{cite web| url =https://www.drugabuse.gov/related-topics/trends-statistics/infographics/teens-e-cigarettes| title =Teens and E-Cigarettes| access-date =2018-12-23| date =2016-02-01| publisher =National Institute on Drug Abuse}}</ref><ref name="Quick Facts on the Risks of E-cigarettes for Kids, Teens, and Young Adults">{{cite web| url =https://www.cdc.gov/tobacco/basic_information/e-cigarettes/Quick-Facts-on-the-Risks-of-E-cigarettes-for-Kids-Teens-and-Young-Adults.html?s_cid=osh-stu-home-slider-004%20| title =Quick Facts on the Risks of E-cigarettes for Kids, Teens, and Young Adults| access-date =2018-12-23| date =2018-12-03| publisher =CDC}}</ref>

The WHO states that "Much of the disease burden and premature mortality attributable to tobacco use disproportionately affect the poor". Of the 1.22 billion smokers, 1 billion live in developing or transitional nations. Rates of smoking have leveled off or declined in the [[Developed country|developed world]].<ref name="pmid17989644">{{cite journal | author = Centers for Disease Control and Prevention (CDC) | title = Cigarette smoking among adults—United States, 2006 | journal = MMWR. Morbidity and Mortality Weekly Report | volume = 56 | issue = 44 | pages = 1157–61 | date = November 2007 | pmid = 17989644 | url = https://www.cdc.gov/mmwr/preview/mmwrhtml/mm5644a2.htm }}</ref> In the [[Developing country|developing world]], however, tobacco consumption was rising by 3.4% per year as of 2002.<ref name="WHO2002FactSheet"/>

The WHO in 2004 projected 58.8 million deaths to occur globally,<ref name = "WHO2004GBD">{{Cite book |last1=Mathers |first1=Colin |author-link=Colin Mathers |last2=Boerma |first2=Ties |last3=Fat |first3=Doris Ma |date=2008 |title=The Global Burden of Disease : 2004 Update |url=https://apps.who.int/iris/handle/10665/43942 |archive-url=https://web.archive.org/web/20220207114854/https://apps.who.int/iris/bitstream/handle/10665/43942/9789241563710_eng.pdf?sequence=1&isAllowed=y |archive-date=7 February 2022 |access-date=2022-10-06 |publisher=[[World Health Organization]] |hdl=10665/43942 |isbn=9789241563710 |oclc=264018380}}</ref>{{rp|8}} from which 5.4 million are tobacco-attributed,<ref name = "WHO2004GBD"/>{{rp|23}} and 4.9 million as of 2007.<ref name="WHO2007FactSheet">{{cite web | url = http://www.wpro.who.int/media_centre/fact_sheets/fs_20070529.htm | title = WHO/WPRO-Tobacco Fact sheet | access-date = 2009-01-01 | date = 2007-05-29 | publisher = World Health Organization Regional Office for the Western Pacific | url-status = dead | archive-url = https://web.archive.org/web/20090207100241/http://www.wpro.who.int/media_centre/fact_sheets/fs_20070529.htm | archive-date = 2009-02-07 }}</ref> As of 2002, 70% of the deaths are in developing countries.<ref name="WHO2007FactSheet"/>

The shift in prevalence of tobacco smoking to a younger demographic, mainly in the developing world, can be attributed to several factors. The tobacco industry spends up to $12.5 billion annually on advertising, which is increasingly geared towards adolescents in the developing world because they are a vulnerable audience for the marketing campaigns. Adolescents have more difficulty understanding the long-term health risks that are associated with smoking and are also more easily influenced by "images of romance, success, sophistication, popularity, and adventure which advertising suggests they could achieve through the consumption of cigarettes". This shift in marketing towards adolescents and even children in the tobacco industry is debilitating to organizations' and countries' efforts to improve child health and mortality in the developing world. It reverses or halts the effects of the work that has been done to improve health care in these countries, and although smoking is deemed as a "voluntary" health risk, the marketing of tobacco towards very impressionable adolescents in the developing world makes it less of a voluntary action and more of an inevitable shift.<ref name="Nichter_1991"/>

Many government regulations have been passed to protect citizens from harm caused by public environmental tobacco smoke. The "Pro-Children Act of 2001" prohibits smoking within any facility that provides health care, day care, library services, or elementary and secondary education to children in the US.<ref>Elementary and Secondary Education | Environmental Tobacco Smoke | Pro-Children Act of 2001 | Non-Smoking Policy for Children's Services | Section 4303</ref> On May 23, 2011, [[New York City]] enforced a smoking ban for all parks, beaches, and pedestrian malls in an attempt to eliminate threats posed to civilians by environmental tobacco smoke.<ref name="pmid21612464">{{cite journal | vauthors = Colgrove J, Bayer R, Bachynski KE | authorlink1=James Colgrove | title = Nowhere left to hide? The banishment of smoking from public spaces | journal = The New England Journal of Medicine | volume = 364 | issue = 25 | pages = 2375–7 | date = June 2011 | pmid = 21612464 | doi = 10.1056/NEJMp1104637 | s2cid = 205107540 | url = https://semanticscholar.org/paper/58c872f587ab535c71a1a045f76544b69ce50126 }}</ref>

== See also ==
* [[Adverse effects of electronic cigarettes]]
* [[E. Cuyler Hammond]]
* [[List of cigarette smoke carcinogens]]
* [[Safety of electronic cigarettes]]

== References ==
{{Reflist|colwidth=30em}}

== Bibliography ==
{{Refbegin}}

* {{Cite book |date=2008 |title=WHO Report on the Global Tobacco Epidemic 2008 : The MPOWER Package. |url=https://apps.who.int/iris/bitstream/handle/10665/43818/9789241596282_eng.pdf?sequence=1&isAllowed=y |archive-url=https://web.archive.org/web/20220121162003/https://apps.who.int/iris/bitstream/handle/10665/43818/9789241596282_eng.pdf?sequence=1&isAllowed=y |archive-date=1 January 2022 |access-date=2022-10-06 |publisher=[[World Health Organization]] |pages=6, 8, 20 |isbn=9789240683112 |oclc=476167599}}
* {{Cite book |last1=Mathers |first1=Colin |author-link=Colin Mathers |last2=Boerma |first2=Ties |last3=Fat |first3=Doris Ma |date=2008 |title=The Global Burden of Disease : 2004 Update |url=https://apps.who.int/iris/handle/10665/43942 |archive-url=https://web.archive.org/web/20220207114854/https://apps.who.int/iris/bitstream/handle/10665/43942/9789241563710_eng.pdf?sequence=1&isAllowed=y |archive-date=7 February 2022 |access-date=2022-10-06 |publisher=[[World Health Organization]] |hdl=10665/43942 |isbn=9789241563710 |oclc=264018380}}
* {{Cite book|url=https://www.cdc.gov/tobacco/data_statistics/sgr/sgr_2004/chapters.htm|title=2004 Surgeon General's Report—The Health Consequences of Smoking|publisher=Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Chronic Disease Prevention and Health Promotion, Office on Smoking and Health|year=2004|location=Washington DC|chapter=Chapter 1: Introduction and Approach to Causal Inference|format=PDF|ref=CITEREF_2004SurgeonGeneral_Chapter1|access-date=2009-05-24|chapter-url=https://www.cdc.gov/tobacco/data_statistics/sgr/2004/pdfs/chapter1.pdf}}
* {{Cite report |url=https://profiles.nlm.nih.gov/spotlight/nn/catalog/nlm:nlmuid-101584932X202-doc# |title=Smoking and Health: Report of the Advisory Committee to the Surgeon General of the United States |last=[[Surgeon General of the United States]] |date=1964 |publisher=[[United States Department of Health and Human Services|Department of Health, Education, and Welfare]] |id=Public Health Service Publication No. 1103 |archive-url=https://web.archive.org/web/20220728033124/https://www.govinfo.gov/content/pkg/GPO-SMOKINGANDHEALTH/pdf/GPO-SMOKINGANDHEALTH.pdf |archive-date=28 July 2022}}
* {{cite web|url=https://www.healthypeople.gov/2020/tools-resources/evidence-based-resource/the-health-consequences-of-involuntary-exposure-to-tobacco-smoke-a-report-of-the-surgeon-general|title=The health consequences of involuntary exposure to tobacco smoke: a report of the Surgeon General|year=2006|publisher=U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Chronic Disease Prevention and Health Promotion, Office on Smoking and Health|location=Atlanta, U.S.|ref=SurgeonGeneralPassiveSmoking2006|access-date=2009-02-15}}
* {{cite web|url=http://tobaccodocuments.org/pm/2073777259-7269.html|title=Cancer Facts and Figures 2004: Basic Cancer Facts|publisher=American Cancer Society|ref=ACS2004|access-date=2009-01-21|url-status=dead|archive-url=https://web.archive.org/web/20090212150945/http://tobaccodocuments.org/pm/2073777259-7269.html|archive-date=2009-02-12}}
* {{cite journal|vauthors=Lichtenstein P, Holm NV, Verkasalo PK, Iliadou A, Kaprio J, Koskenvuo M, Pukkala E, Skytthe A, Hemminki K|title=Environmental and heritable factors in the causation of cancer—analyses of cohorts of twins from Sweden, Denmark, and Finland|journal=The New England Journal of Medicine|volume=343|issue=2|pages=78–85|date=July 2000|pmid=10891514|doi=10.1056/NEJM200007133430201|ref=Lichtenstein2000}}
* {{cite journal|vauthors=Montesano R, Hall J|title=Environmental causes of human cancers|journal=European Journal of Cancer|volume=37 | issue = Suppl 8|pages=S67–87|date=October 2001|pmid=11602374|doi=10.1016/S0959-8049(01)00266-0|ref=Montesano2001}}

{{Refend}}

== External links ==
{{Sister project links|Tobacco}}
* [https://web.archive.org/web/20120302234733/http://tobaccofree.nzdis.org/ Tobacco Free awareness action – How many people smoke in cars]

{{Smoking by country}}

{{Health effects of}}

{{Cigarettes}}

[[Category:Health effects of tobacco| ]]