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Secondhand Smoke

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Exposure to secondhand tobacco smoke (SHS) was one of the leading risk factors for deaths globally in 2019, accounting for approximately 1.3 million deaths and contributing to 37 million Disability-Adjusted life years (DALYs), with 11.2% of the burden in children under the age of 5 years.

Secondhand smoke (SHS) includes the smoke from the burning end of a cigarette or other smoked tobacco products such as pipes, cigars, etc., and the smoke exhaled by the smoker. It is also referred to as passive smoking, environmental tobacco smoke, and tobacco smoke pollution.

SHS contains more than 7,000 chemicals, including irritants, systemic toxicants, mutagens, carcinogens, and reproductive and development toxicants. More than 70 of these compounds are carcinogens, which has led the US Environmental Protection Agency and the International Agency for Research on Cancer to classify SHS as a group A and group 1 carcinogen, respectively, indicating the most hazardous cancer-causing compounds.

It is widely recognized through scientific evidence that there is no safe level of exposure to SHS. It remains in the air for hours after smoked tobacco has been extinguished and can cause or contribute to various adverse health effects in adults and children, even if exposed for a short time.

Exposure to secondhand smoke can lead to lung cancer, acute and chronic coronary heart disease (CHD), and eye and nasal irritation in adults. Research also shows that the risks for CHD from passive smoking are essentially indistinguishable from active smoking. Children can suffer from asthma exacerbation, bronchitis and pneumonia, chronic middle ear infection, and chronic respiratory symptoms. Pregnant women exposed to SHS are more likely to experience stillbirths and have newborns with congenital malformations and lower birth weights; infants are at a significantly higher risk of sudden infant death syndrome (SIDS).

The World Health Organization (WHO) Report on the Global Tobacco Epidemic 2023 (RGTE) presents smoke-free legislation information for 195 countries and as of 2022, 2.1 billion people in 74 countries are covered by complete smoke-free indoor public places, workplaces, and public transport. These 74 countries include 21 high-income countries, 45 middle income countries, and 8 low-income countries. While these 74 countries (38%) show best practice levels in comprehensive smoke-free bans, there are still 35% of countries, with partial smoke-free ban environments. The remaining 53 countries (27%) fail to comprehensively protect people from secondhand smoke by having complete absence of or minimal smoking bans. Results from the Global Youth Tobacco Survey (GYTS) conducted in 142 countries from 2010 to 2018 indicate that adolescents aged 12-16 years were widely exposed (on ≥1 day in the past 7 days) to SHS in any place (62.9%), at home (33.3%), and in public places (57.6%).

Evidence shows persistent disparities in secondhand smoke exposure by ethnicity, education, and income level. In the U.S., non-Hispanic Black Americans and families living below the poverty level or in multi-unit housing are more likely than other groups to be exposed to SHS. Typically, people with lower educational attainment are less knowledgeable about SHS exposure risks. Awareness is also generally lower in low-income countries compared to high-income countries.

The dangers from SHS also extend to the e-cigarette aerosols that users exhale, which contain harmful and potentially harmful substances, including nicotine, heavy metals, and carcinogens. Though more research on the harm profile of second aerosol is needed, it is clear that these aerosols should be included in comprehensive smoke-free legislation in the same way as secondhand smoke.

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Institute for Health Metrics and Evaluation. Secondhand smoke risk. See

Smoke-free policy coverage:

WHO report on the global tobacco epidemic, 2023: protect people from tobacco smoke. Geneva: World Health Organization; 2023. Licence: CC BY-NC-SA 3.0 IGO.

Youth smoking:

Global Youth Tobacco Surveys (various years). See

Ma, C., Heiland, E. G., Li, Z., Zhao, M., Liang, Y., & Xi, B. (2021). Global trends in the prevalence of secondhand smoke exposure among adolescents aged 12–16 years from 1999 to 2018: an analysis of repeated cross-sectional surveys. The Lancet Global Health, 9(12), e1667-e1678.

Tobacco smoke as a carcinogen:

International Agency for Research on Cancer (IARC). Smoke, Tobacco, and Involuntary Smoking. In IARC monographs on the evaluation of carcinogenic risks to humans. IARC, Lyon 1 (2004): 1-1452.

US Environmental Protection Agency. Respiratory Health Effects of Passive Smoking: Lung Cancer and Other Disorders” (EPA 600/6/90/006F) (December 1992).

Exposure to SHS by discrete groups:

Homa DM, Neff LJ, King BA, Caraballo RS, Bunnell RE, Babb SD, Garrett BE, Sosnoff CS, Wang L. Vital signs: disparities in nonsmokers’ exposure to secondhand smoke—United States, 1999–2012. Morbidity and Mortality Weekly Report. 2015 Feb 2;64(4):103.

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