Harmful effects of SHS on health

Many US government reports, going back to the 1972 Surgeon General’s report ‘The Health Consequences of Smoking’, have discussed the harmful effects of SHS. The National Research Council and the Environmental Protection Agency (EPA) have also independently assessed the health effects of exposure to ETS ( figure 1 ).

The EPA report, published in 1992, confirmed that the respiratory effects of ETS included:

Constituent Emissions in SS per cigarette Amount in SHS per m 3
Benzene 163–353 μg 4.2–63.7 μg
Benzo[a]pyrene 45–103 ng 0.37–1.7 ng
NNK 201–1440 ng 0.2–29.3 ng
4-Aminobiphenyl 11.4–18.8 ng  
2-Naphthylamine 63.1–128 ng  
1,3-Butadiene 98–205 μg 0.3–40 μg
Formaldehyde 233–485 μg 143 μg
Table 1 – Carcinogens in sidestream smoke (SS) and second-hand smoke (SHS) from cigarettes. NNK:
4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone. 
  • Lung cancer in nonsmoking adults. Passive smoking is causally associated with lung cancer in adults, and thus ETS, given the weight of evidence, belongs in the category of compounds classified by the EPA as Group A (known human) carcinogens.
  • Non-cancer respiratory diseases and disorders.
    • Exposure of children to ETS from parental smoking is causally associated with: increased prevalence of respiratory symptoms of irritation (cough, sputum, and wheeze); increased prevalence of middle ear effusion (a sign of middle ear disease); and a small but statistically significant reduction in lung function as tested by objective measures of lung capacity.
    • exposure to ETS is causally associated with additional episodes and increased severity of asthma in children who already have the disease.
    • The epidemiological evidence is suggestive but not conclusive that ETS exposure increases the number of new cases of asthma in children who have not previously shown symptoms. Based on this evidence and the known effects of ETS on the immune system and lungs (e.g. atopy and airway hyperresponsiveness) the report concluded that ETS is a risk factor for the induction of asthma in previously asymptomatic children. Data suggest that relatively high levels of exposure are required to induce new cases of asthma in children.
  • Subtle but significant effects of passive smoking on the respiratory health of nonsmoking adults, including coughing, phlegm production, chest discomfort and reduced lung function.

At the time that the early reports were published, there was some uncertainty about the relationship of SHS to sudden infant death syndrome (SIDS), upper respiratory tract infections and middle ear infections in children. However, by 2006, when the US Surgeon General published ‘The Health Consequences of Involuntary Exposure to Tobacco Smoke’, it was possible to state clearly that:

  • SHS causes premature death and disease in children and in adults who do not smoke.
  • Children exposed to SHS are at an increased risk of SIDS, acute respiratory infections, ear problems and more severe asthma. Smoking by parents causes respiratory symptoms and slows lung growth in their children.
  • SHS has immediate adverse effects on the cardiovascular system of adults and causes coronary heart disease and lung cancer.
  • The scientific evidence indicates that there is no risk-free level of exposure to SHS.
  • Many millions of Americans, both children and adults, are still exposed to SHS in their homes and workplaces despite substantial progress in tobacco control.
  • Eliminating smoking in indoor spaces fully protects nonsmokers from exposure to SHS. Separating smokers from nonsmokers, cleaning the air and ventilating buildings, however, cannot prevent nonsmokers being exposed to SHS.

See the entire Passive smoking Chapter