Editing Cigarette (section)

== Health effects ==
=== Smokers ===
{{Main|Health effects of tobacco}}
[[File:MODOArtistas.jpg|thumb|Artistas brand cigarette package of Mexico from the [[Museo del Objeto del Objeto]] collection]]
[[File:BahnhofsuhrZuerich RZ.jpg|thumb|A 2024 study estimated that each cigarette reduces [[life expectancy]] by 20 minutes]]
The harm from smoking comes from the many toxic chemicals in the natural tobacco leaf and those formed in smoke from burning tobacco.<ref>{{cite web|publisher=Centers for Disease Control and Prevention|date=March 5, 2018|title=2014 SGR: The Health Consequences of Smoking—50 Years of Progress|accessdate=November 25, 2019|url=https://www.cdc.gov/tobacco/data_statistics/sgr/50th-anniversary/index.htm|archiveurl=https://web.archive.org/web/20131201130315/https://www.cdc.gov/tobacco/data_statistics/sgr/50th-anniversary/index.htm|archivedate=December 1, 2013}}</ref> A 2024 study estimated that each cigarette reduces [[life expectancy]] by 20 minutes.<ref>{{cite news|author1=Sarah Jackson |author2=Martin Jarvis|author3=[[Robert West (psychologist)|Robert West]]|title=The price of a cigarette: 20 minutes of life?|url=https://onlinelibrary.wiley.com/doi/10.1111/add.16757|journal=[[Addiction (journal)|Addiction]]|date=29 December 2024 |doi=10.1111/add.16757|access-date=22 January 2025}}</ref><ref>{{cite news|author=Sample, Ian|title=Single cigarette takes 20 minutes off life expectancy, study finds|url=https://www.theguardian.com/society/2024/dec/30/single-cigarette-takes-20-minutes-off-life-expectancy-study|newspaper=[[The Guardian]]|date=30 December 2024|access-date=22 January 2025}}</ref> Humans continue to smoke because [[nicotine]], the primary psychoactive chemical in cigarettes, is highly addictive.<ref>{{cite web |url=http://www.heart.org/HEARTORG/GettingHealthy/QuitSmoking/QuittingSmoking/Why-is-it-so-hard-to-quit_UCM_324053_Article.jsp |title=Why is it so hard to quit? |publisher=Heart.org |access-date=March 25, 2012 |archive-date=April 2, 2012 |archive-url=https://web.archive.org/web/20120402173038/http://www.heart.org/HEARTORG/GettingHealthy/QuitSmoking/QuittingSmoking/Why-is-it-so-hard-to-quit_UCM_324053_Article.jsp |url-status=live }}</ref> Cigarettes, like narcotics, have been described as "strategically addictive", with the addictive properties being a core component of the business strategy.<ref>{{cite web|last=Day|first=Ruby|title=Strategically Addictive Drugs|url=https://www.innowiki.org/strategically-addictive-drugs/|access-date=September 4, 2020|archive-date=October 30, 2020|archive-url=https://web.archive.org/web/20201030035000/https://www.innowiki.org/strategically-addictive-drugs/|url-status=live}}</ref> About half of smokers die from a smoking-related cause.<ref name="fact-sheets"/><ref name="bmj.bmjjournals.com.331">{{cite journal |last1=Doll |first1=R. |last2=Peto |first2=R. |last3=Boreham |first3=J. |last4=Sutherland |first4=I. |year=2004 |title=Mortality in relation to smoking: 50 years' observations on male British doctors |journal=BMJ (Clinical Research Ed.) |volume=328 |issue=7455 |pages=1519 |doi=10.1136/bmj.38142.554479.AE |pmc=437139 |pmid=15213107}}</ref><ref name="m11">{{cite web |title=Archived copy |url=http://www.nyc.gov/html/doh/downloads/pdf/chi/chi24-4-pktguide.pdf |archive-url=https://web.archive.org/web/20091229042543/http://www.nyc.gov/html/doh/downloads/pdf/chi/chi24-4-pktguide.pdf |archive-date=December 29, 2009 |access-date=November 13, 2009}}</ref> Smoking harms nearly every organ of the body. Smoking leads most commonly to diseases affecting the heart,<ref name="Nicotine Addiction">{{cite journal |last1=Benowitz |first1=Neal L. |title=Nicotine Addiction |journal=The New England Journal of Medicine |date=June 17, 2010 |volume=362 |issue=24 |pages=2295–2303 |doi=10.1056/NEJMra0809890 |pmid=20554984 |issn=0028-4793|pmc=2928221 }}</ref> liver, and lungs, being a major risk factor for [[myocardial infarction|heart attacks]], [[stroke]]s, [[chronic obstructive pulmonary disease]] (COPD) (including [[chronic obstructive pulmonary disease|emphysema]] and [[chronic obstructive pulmonary disease|chronic bronchitis]]), and [[cancer]]<ref name="Nicotine Addiction"/><ref name="framework-treaty">{{cite web |date=February 27, 2005 |title=WHO Framework Convention on Tobacco Control |url=https://www.who.int/tobacco/framework/WHO_FCTC_english.pdf |archive-url=https://web.archive.org/web/20050906213831/http://www.who.int/tobacco/framework/WHO_FCTC_english.pdf |archive-date=September 6, 2005 |access-date=January 12, 2009 |publisher=[[World Health Organization]] |quote=Parties recognize that scientific evidence has unequivocally established that exposure to tobacco has the potential to cause death, disease and disability}}</ref><ref name="sg-report">{{cite web |date=June 27, 2006 |title=The Health Consequences of Involuntary Exposure to Tobacco Smoke: A Report of the Surgeon General |url=https://www.ncbi.nlm.nih.gov/books/NBK44324/ |access-date=June 16, 2014 |publisher=[[Surgeon General of the United States]] |pmid=20669524 |quote=Secondhand smoke exposure causes disease and premature death in children and adults who do not smoke |author1=Office on Smoking Health (US) |archive-date=February 15, 2017 |archive-url=https://web.archive.org/web/20170215064658/https://www.ncbi.nlm.nih.gov/books/NBK44324/ |url-status=live }}</ref><ref name="calepa2005">{{cite report |url=http://repositories.cdlib.org/context/tc/article/1194/type/pdf/viewcontent/ |title=Proposed Identification of Environmental Tobacco Smoke as a Toxic Air Contaminant |last1=Board |date=June 24, 2005 |publisher=[[California Environmental Protection Agency]] |access-date=January 12, 2009 |via=University of California San Francisco: Center for Tobacco Control Research and Education}}</ref><ref name="iarc-monograph">{{cite book |url=http://monographs.iarc.fr/ENG/Monographs/vol83/index.php |title=Tobacco Smoke and Involuntary Smoking |publisher=[[International Agency for Research on Cancer]] |year=2004 |isbn=9789283215837 |format=PDF |quote=There is sufficient evidence that involuntary smoking (exposure to secondhand or 'environmental' tobacco smoke) has the potential to cause lung cancer in humans |access-date=January 12, 2009 |archive-date=June 7, 2018 |archive-url=https://web.archive.org/web/20180607085206/http://monographs.iarc.fr/ENG/Monographs/vol83/index.php |url-status=live }}</ref> (particularly [[lung cancer]], [[Laryngeal cancer|cancers of the larynx and mouth]], and [[pancreatic cancer]]). It also causes peripheral vascular disease and [[hypertension]]. Children born to women who smoke during pregnancy are at higher risk of congenital disorders, cancer, respiratory disease, and sudden death.<ref name="CsordasBernhard2013">{{cite journal |last1=Csordas |first1=Adam |last2=Bernhard |first2=David |year=2013 |title=The biology behind the atherothrombotic effects of cigarette smoke |journal=Nature Reviews Cardiology |volume=10 |issue=4 |pages=219–230 |doi=10.1038/nrcardio.2013.8 |issn=1759-5002 |pmid=23380975 |s2cid=25491622}}</ref> On average, each cigarette smoked is estimated to shorten life by 11 minutes.<ref name="m11"/><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=December 31, 1999 |access-date=March 25, 2012 |archive-date=December 2, 2008 |archive-url=https://web.archive.org/web/20081202074346/http://news.bbc.co.uk/1/hi/health/583722.stm |url-status=live }}</ref><ref>{{cite journal|title=Time for a smoke? One cigarette reduces your life by 11 minutes |journal=BMJ |doi=10.1136/bmj.320.7226.53 |volume=320 |year=2000 |page=53 | last1 = Shaw | first1 = M.|issue=7226 |pmid=10617536 |pmc=1117323 }}</ref> Starting smoking earlier in life and smoking cigarettes higher in [[Tar (tobacco residue)|tar]] increases the risk of these diseases. The [[World Health Organization]] <!-- (WHO) --> estimates that tobacco causes 8 million deaths each year as of 2019<ref name="fact-sheets">{{Cite web|url=https://www.who.int/news-room/fact-sheets/detail/tobacco|title=Tobacco|website=www.who.int|language=en|access-date=July 17, 2019|archive-date=July 9, 2021|archive-url=https://web.archive.org/web/20210709165139/https://www.who.int/news-room/fact-sheets/detail/tobacco|url-status=live}}</ref> and 100 million deaths over the course of the 20th century.<ref name="urlwww.who.int">{{cite web | url =https://www.who.int/entity/tobacco/mpower/mpower_report_prevalence_data_2008.pdf | archive-url =https://wayback.archive-it.org/all/20080910041812/http://www.who.int/entity/tobacco/mpower/mpower_report_prevalence_data_2008.pdf | archive-date =September 10, 2008 | title = WHO Report on the Global Tobacco Epidemic | year = 2008 | publisher = World Health Organization }}</ref> Cigarettes produce an aerosol containing over 4,000 chemical compounds, including nicotine, carbon monoxide, acrolein, and oxidant substances.<ref name=CsordasBernhard2013/><ref name="Smoking Deformities">{{cite web |title=Smoking While Pregnant Causes Finger, Toe Deformities |url=https://www.sciencedaily.com/releases/2006/01/060106122922.htm |access-date=March 6, 2007 |work=Science Daily |archive-date=March 4, 2007 |archive-url=https://web.archive.org/web/20070304070934/http://www.sciencedaily.com/releases/2006/01/060106122922.htm |url-status=live }}</ref> Over 70 of these are [[carcinogen]]s.<ref name="IARC">{{cite book |title=Personal Habits and Indoor Combustions |publisher=International Agency for Research on Cancer |year=2012 |volume=100E |page=44 |chapter=Tobacco Smoking |chapter-url=https://monographs.iarc.fr/wp-content/uploads/2018/06/mono100E-6.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://monographs.iarc.fr/wp-content/uploads/2018/06/mono100E-6.pdf |archive-date=2022-10-09 |url-status=live}}</ref>

The most important chemical compounds [[carcinogenesis|causing cancer]] are those that produce DNA damage since such damage appears to be the primary underlying cause of cancer.<ref name="pmid18403632">{{cite journal |vauthors=Kastan MB |title=DNA damage responses: mechanisms and roles in human disease: 2007 G.H.A. Clowes Memorial Award Lecture |journal=Mol. Cancer Res. |volume=6 |issue=4 |pages=517–24 |year=2008 |pmid=18403632 |doi=10.1158/1541-7786.MCR-08-0020 |doi-access=free }}</ref> Cigarette smoking results in [[oxidative stress]] and oxidative [[DNA damage (naturally occurring)|DNA damage]].  DNA damage can be estimated by measuring urinary 8-hydroxy-2’-deoxyguanosine (8-OHdG) and [[oxoguanine glycosylase|8-oxoguanine DNA glycosylase]] (OGG1).<ref name = Ajileye2024>Ajileye AB, Akinbo FO. Oxidative DNA damage estimated by urinary 8-Hydroxy-2’ –Deoxyguanosine          (8-OHdG) and 8-Oxoguanine DNA Glycosylase (OGG1) in cigarette and non-cigarette smokers in          South West Nigeria. Journal of Cellular Biotechnology. 2024;10(1):25-34. doi:10.3233/JCB-230120</ref>  DNA damage was found in a population study to be significantly increased in 250 cigarette smokers compared to 200 non-cigarette smokers.<ref name = Ajileye2024/> Cunningham et al.<ref name=Cunningham>{{cite journal |vauthors=Cunningham FH, Fiebelkorn S, Johnson M, Meredith C |title=A novel application of the Margin of Exposure approach: segregation of tobacco smoke toxicants |journal=Food Chem. Toxicol. |volume=49 |issue=11 |pages=2921–33 |year=2011 |pmid=21802474 |doi=10.1016/j.fct.2011.07.019 }}</ref> combined the microgram weight of the compound in the smoke of one cigarette with the known [[Genotoxicity|genotoxic]] effect per microgram to identify the most [[Carcinogenesis|carcinogenic]] compounds in cigarette smoke. The seven most important carcinogens in tobacco smoke are shown in the table, along with DNA alterations they cause.
{| class="wikitable sortable"
|+'''The most [[Genotoxicity|genotoxic]] cancer causing chemicals in cigarette smoke'''
!width="75"|Compound
!width="75"|Micrograms per cigarette
!width="225"|Effect on DNA
!width="10"| {{Refh}}
|-
|[[Acrolein]]
|align="right"|122.4
|Reacts with deoxyguanine and forms DNA crosslinks, DNA-protein crosslinks and DNA adducts
|<ref name="pmid20158384">{{cite journal |vauthors=Liu XY, Zhu MX, Xie JP |title=Mutagenicity of acrolein and acrolein-induced DNA adducts |journal=Toxicol. Mech. Methods |volume=20 |issue=1 |pages=36–44 |year=2010 |pmid=20158384 |doi=10.3109/15376510903530845 |s2cid=8812192 }}</ref>
|-
|[[Formaldehyde]]
|align="right"|60.5
|DNA-protein crosslinks causing chromosome deletions and re-arrangements
|<ref name="pmid11971987">{{cite journal |vauthors=Speit G, Merk O |title=Evaluation of mutagenic effects of formaldehyde in vitro: detection of crosslinks and mutations in mouse lymphoma cells |journal=Mutagenesis |volume=17 |issue=3 |pages=183–7 |year=2002 |pmid=11971987 |doi= 10.1093/mutage/17.3.183|doi-access=free }}</ref>
|-
|[[Acrylonitrile]]
|align="right"|29.3
|Oxidative stress causing increased [[8-Oxo-2'-deoxyguanosine|8-oxo-2'-deoxyguanosine]]
|<ref name="pmid19546159">{{cite journal |vauthors=Pu X, Kamendulis LM, Klaunig JE |title=Acrylonitrile-induced oxidative stress and oxidative DNA damage in male Sprague-Dawley rats |journal=Toxicol. Sci. |volume=111 |issue=1 |pages=64–71 |year=2009 |pmid=19546159 |pmc=2726299 |doi=10.1093/toxsci/kfp133 }}</ref>
|-
|[[1,3-Butadiene|1,3-butadiene]]
|align="right"|105.0
|Global loss of DNA methylation (an [[Cancer epigenetics|epigenetic]] effect) as well as DNA adducts
|<ref name="pmid21602187">{{cite journal |vauthors=Koturbash I, Scherhag A, Sorrentino J, Sexton K, Bodnar W, Swenberg JA, Beland FA, Pardo-Manuel Devillena F, Rusyn I, Pogribny IP |title=Epigenetic mechanisms of mouse interstrain variability in genotoxicity of the environmental toxicant 1,3-butadiene |journal=Toxicol. Sci. |volume=122 |issue=2 |pages=448–56 |year=2011 |pmid=21602187 |pmc=3155089 |doi=10.1093/toxsci/kfr133 }}</ref>
|-
|[[Acetaldehyde]]
|align="right"|1448.0
|Reacts with deoxyguanine to form DNA adducts
|<ref name="pmid21604744">{{cite journal |vauthors=Garcia CC, Angeli JP, Freitas FP, Gomes OF, de Oliveira TF, Loureiro AP, Di Mascio P, Medeiros MH |title=[13C2]-Acetaldehyde promotes unequivocal formation of 1,N2-propano-2'-deoxyguanosine in human cells |journal=J. Am. Chem. Soc. |volume=133 |issue=24 |pages=9140–3 |year=2011 |pmid=21604744 |doi=10.1021/ja2004686 |url=https://figshare.com/articles/_sup_13_sup_C_sub_2_sub_Acetaldehyde_Promotes_Unequivocal_Formation_of_1_i_N_i_sup_2_sup_Propano_2_deoxyguanosine_in_Human_Cells/2639098 |access-date=December 1, 2019 |archive-date=November 6, 2020 |archive-url=https://web.archive.org/web/20201106102427/https://figshare.com/articles/_sup_13_sup_C_sub_2_sub_Acetaldehyde_Promotes_Unequivocal_Formation_of_1_i_N_i_sup_2_sup_Propano_2_deoxyguanosine_in_Human_Cells/2639098 |url-status=live |url-access=subscription }}</ref>
|-
|[[Ethylene oxide]]
|align="right"|7.0
|Hydroxyethyl DNA adducts with adenine and guanine
|<ref name="pmid19477295">{{cite journal |vauthors=Tompkins EM, McLuckie KI, Jones DJ, Farmer PB, Brown K |title=Mutagenicity of DNA adducts derived from ethylene oxide exposure in the pSP189 shuttle vector replicated in human Ad293 cells |journal=Mutat. Res. |volume=678 |issue=2 |pages=129–37 |year=2009 |pmid=19477295 |doi=10.1016/j.mrgentox.2009.05.011 |bibcode=2009MRGTE.678..129T }}</ref>
|-
|[[Isoprene]]
|align="right"|952.0
|Single and double strand breaks in DNA
|<ref name="pmid17317274">{{cite journal |vauthors=Fabiani R, Rosignoli P, De Bartolomeo A, Fuccelli R, Morozzi G |title=DNA-damaging ability of isoprene and isoprene mono-epoxide (EPOX I) in human cells evaluated with the comet assay |journal=Mutat. Res. |volume=629 |issue=1 |pages=7–13 |year=2007 |pmid=17317274 |doi=10.1016/j.mrgentox.2006.12.007 |bibcode=2007MRGTE.629....7F }}</ref>
|}
{| class="wikitable"
|+Number of Current and Expected Smokers, and Expected Deaths<ref>{{Citation |last1=Jha |first1=Prabhat |title=Global Hazards of Tobacco and the Benefits of Smoking Cessation and Tobacco Taxes |date=2015 |url=http://www.ncbi.nlm.nih.gov/books/NBK343639/ |work=Cancer: Disease Control Priorities, Third Edition (Volume 3) |editor-last=Gelband |editor-first=Hellen |access-date=2023-11-20 |place=Washington (DC) |publisher=The International Bank for Reconstruction and Development / The World Bank |isbn=978-1-4648-0349-9 |pmid=26913345 |last2=MacLennan |first2=Mary |last3=Chaloupka |first3=Frank J. |last4=Yurekli |first4=Ayda |last5=Ramasundarahettige |first5=Chintanie |last6=Palipudi |first6=Krishna |last7=Zatońksi |first7=Witold |last8=Asma |first8=Samira |last9=Gupta |first9=Prakash C. |doi=10.1596/978-1-4648-0349-9_ch10 |editor2-last=Jha |editor2-first=Prabhat |editor3-last=Sankaranarayanan |editor3-first=Rengaswamy |editor4-last=Horton |editor4-first=Susan}}</ref>
!Country
!Current and future smokers,
ages 15+ (millions)
!Approximate number of deaths in current
and future smokers younger than 35, unless they quit (millions)
|-
|China (2010)
|193
|97
|-
|Indonesia (2011)
|58
|29
|-
|Russian Federation
(2008)
|32
|16
|-
|United States (2011)
|26
|13
|-
|India (2009)
|95
|48
|-
|Bangladesh (2009)
|25
|13
|}
"[[Ulcerative colitis]] is a condition of nonsmokers in which nicotine is of therapeutic benefit."<ref>{{Cite journal
| doi = 10.1046/j.1365-2036.2000.00847.x
| last1 = Green | first1 = J. T.
| last2 = Richardson | first2 = C.
| last3 = Marshall | first3 = R. W.
| last4 = Rhodes | first4 = J.
| last5 = McKirdy | first5 = H. C.
| last6 = Thomas | first6 = G. A.
| last7 = Williams | first7 = G. T.
| s2cid = 21358737 | title = Nitric oxide mediates a therapeutic effect of nicotine in ulcerative colitis
| journal = Alimentary Pharmacology & Therapeutics
| volume = 14
| issue = 11
| pages = 1429–1434
| year = 2000
| pmid = 11069313
| doi-access = free
}}</ref> A recent review of the available scientific literature concluded that the apparent decrease in [[Alzheimer disease]] risk may be simply because smokers tend to die before reaching the age at which it 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 nonsmokers to survive to the age of 80.<ref name="alzheimer-almeida">{{Cite journal | doi = 10.1046/j.1360-0443.2002.00016.x | title = Smoking as a risk factor for Alzheimer's disease: contrasting evidence from a systematic review of case-control and cohort studies | year = 2002 |vauthors=Almeida OP, Hulse GK, Lawrence D, Flicker L | s2cid = 22936675 | journal = Addiction | volume = 97 | pages = 15–28| pmid = 11895267 | issue = 1 | doi-access = free }}</ref>

==== Gateway theory ====
A very strong argument has been made about the association between adolescent exposure to nicotine by smoking conventional cigarettes and the subsequent onset of using other dependence-producing substances.{{sfn|SGUS|2016|p=106; Chapter 3}} Strong temporal and dose-dependent associations have been reported, and a plausible biological mechanism (via rodent and human modeling) suggests that long-term changes in the neural reward system take place as a result of adolescent smoking.{{sfn|SGUS|2016|p=106; Chapter 3}} Adolescent smokers of conventional cigarettes have disproportionately high rates of comorbid substance use, and longitudinal studies have suggested that early adolescent smoking may be a starting point or "[[Gateway drug theory|gateway]]" for substance use later in life, with this effect more likely for persons with [[attention deficit hyperactivity disorder]] (ADHD).{{sfn|SGUS|2016|p=106; Chapter 3}} Although factors such as genetic comorbidity, innate propensity for risk-taking, and social influences may underlie these findings, both human neuroimaging and animal studies suggest a neurobiological mechanism also plays a role.{{sfn|SGUS|2016|p=106; Chapter 3}} In addition, behavioral studies in adolescent and young adult smokers have revealed an increased propensity for risk-taking, both generally and in the presence of peers, and neuroimaging studies have shown altered frontal neural activation during a risk-taking task as compared with nonsmokers.{{sfn|SGUS|2016|p=106; Chapter 3}} In 2011, Rubinstein and colleagues used neuroimaging to show decreased brain response to a natural reinforcer (pleasurable food cues) in adolescent light smokers (1–5 cigarettes per day), with their results highlighting the possibility of neural alterations consistent with nicotine dependence and altered brain response to reward even in adolescent low-level smokers.{{sfn|SGUS|2016|p=106; Chapter 3}}

=== Second-hand smoke ===
[[Passive smoking|Second-hand smoke]] is a mixture of smoke from the burning end of a cigarette and the smoke exhaled from the lungs of smokers. It is involuntarily inhaled, lingers in the air for hours after cigarettes have been extinguished, and can 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.lungusa.org/site/pp.asp?c=dvLUK9O0E&b=35422#one |title=Secondhand Smoke |date=June 2007 |publisher=American Lung Association |access-date=May 6, 2012 |archive-url=https://web.archive.org/web/20091016220328/http://www.lungusa.org/site/pp.asp?c=dvLUK9O0E&b=35422 |archive-date=October 16, 2009 }}</ref> Nonsmokers who are exposed to second-hand smoke at home or work 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 nonsmokers.<ref>{{cite web |url=http://www.tobaccofreefloridanewsroom.com/?cat=6 |title=Centers for Disease Control & Prevention Fact Sheets |publisher=[[Tobacco Free Florida]] |access-date=January 2, 2013 |archive-date=December 2, 2008 |archive-url=https://web.archive.org/web/20081202074323/http://www.tobaccofreefloridanewsroom.com/?cat=6 |url-status=live }}</ref> Sudden infant death syndrome, ear infections, respiratory infections, and asthma attacks can occur in children who are exposed to second-hand smoke.<ref name="Secondhand Smoke">{{cite web |url=http://www.cancer.org/Cancer/CancerCauses/TobaccoCancer/secondhand-smoke |title=Secondhand Smoke |publisher=Cancer.org |access-date=March 25, 2012 |archive-date=January 7, 2017 |archive-url=https://web.archive.org/web/20170107025355/http://www.cancer.org/cancer/cancercauses/tobaccocancer/secondhand-smoke |url-status=live }}</ref><ref name="NCI">{{cite web |url=http://www.cancer.gov/cancertopics/factsheet/Tobacco/ETS |title=Secondhand Smoke and Cancer - National Cancer Institute |publisher=Cancer.gov |date=August 18, 2005 |access-date=March 25, 2012 |archive-date=March 25, 2012 |archive-url=https://web.archive.org/web/20120325183133/http://cancer.gov/cancertopics/factsheet/Tobacco/ETS |url-status=live }}</ref><ref name="Smoking and Tobacco">{{cite web |url=https://www.cdc.gov/tobacco/data_statistics/fact_sheets/secondhand_smoke/general_facts/index.htm |title=CDC - Fact Sheet - Secondhand Smoke Facts - Smoking & Tobacco Use |publisher=Cdc.gov |access-date=March 25, 2012 |archive-date=August 19, 2022 |archive-url=https://web.archive.org/web/20220819034536/https://www.cdc.gov/tobacco/data_statistics/fact_sheets/secondhand_smoke/general_facts/index.htm |url-status=live }}</ref> Scientific evidence shows that no level of exposure to second-hand smoke is safe.<ref name="Secondhand Smoke"/><ref name="NCI"/>