Secondhand Smoke

Secondhand Smoke Facts

  • Secondhand smoke is tobacco smoke that is breathed in by someone who is not smoking themselves.
  • It occurs when a person is in the vicinity of a person who is smoking.
  • Secondhand smoke is a mixture of the smoke from the tobacco product itself (termed sidestream smoke) and exhaled smoke from the smoker (known as mainstream smoke).
  • The same chemicals, toxins, and cancer-causing substances are present in secondhand smoke as in active smoking; the person who inhales secondhand smoke is exposed to the same toxins as the smoker.
  • Secondhand smoke is known to carry definite health risks for both adults and children. An increased risk of lung cancer is just one of the hazardous health effects of secondhand smoke.

Secondhand Smoke Causes

Any tobacco product has the potential to cause dangers due to secondhand smoke, but cigarettes are the most common sources of secondhand smoke. Exposure to secondhand smoke can occur in the home, workplace, or in public places. Children exposed to secondhand smoke in the home are at particular risk for health problems related to tobacco smoke, as are nonsmokers who reside with smokers.

Secondhand Smoke Health Risks

  • Secondhand smoke contains hundreds of harmful chemicals.
  • About 70 cancer-causing substances have been identified in secondhand smoke, and secondhand smoke has been classified as a "known human carcinogen" by the U.S. Environmental Protection Agency (EPA). A carcinogen is a chemical substance that has been proven to cause cancer.
  • Besides causing cancers, secondhand smoke carries multiple additional health risks for both adults and children. These risks are outlined in the following sections.


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Does Secondhand Smoke Cause Cancer?

  • People who do not smoke but reside with a smoker have a greater chance of developing lung cancer than typical nonsmokers.
  • Each year in the United States, over 7,000 people die as a result of lung cancer that develops as a result of secondhand smoke, or passive smoking.

Effects Secondhand Smoke and Heart Disease

Effects Secondhand Smoke and Other Lung Diseases

  • Lung function is compromised in those who are continuously exposed to secondhand smoke.
  • Symptoms such as coughing and chest congestion are more common in those exposed to passive smoke than in nonsmokers who reside in smoke free environments.
  • The respiratory effects of secondhand smoke are particularly dangerous to infants and young children.
  • Babies exposed to secondhand smoke can develop serious respiratory infections. Every year, passive smoking is believed to cause 150,000 to 300,000 lung infections (such as pneumonia and bronchitis) in children younger than 18 months of age in the U.S.

Effects Secondhand Smoke on Children

  • Lung disease and respiratory infections are not the only risks suffered by children and infants who are exposed to passive smoke.
  • Passive smoking also worsens asthma in children, increases their risk for the development of middle ear infections, and increases the risk for sudden infant death syndrome (SIDS).

Secondhand Smoke and Breast Cancer

  • Even though breast cancer rates are not known to be increased in active smokers, some research points to a possible effect of passive smoke on breast cancer development.
  • Tobacco smoke does contain chemicals that have been shown to cause breast cancer in animal models.
  • It is also known that chemicals from tobacco smoke are able to accumulate in breast tissue and breast milk.
  • Whether secondhand smoke actually increases the risk of breast cancer has not been conclusively determined, but the U.S. Surgeon General's report concluded that there is "suggestive but not sufficient" evidence of a link in 2006.

Secondhand Smoke Safe Levels

All secondhand smoke is harmful. The greatest risks come with greater or more prolonged exposures, but a true safe level of exposure has not been defined. Therefore, one should avoid all exposure to secondhand smoke when possible.

Reducing Secondhand Smoke Exposure

Secondhand smoke is a known contributor to premature death in both adults and children. If you are a smoker, quitting smoking is the best way to protect your children, other family members, and friends from the serious health risks of passive smoking. Nonsmokers and smokers who wish to protect their families from these risks should not allow themselves or others to smoke in their homes.

In the U.S. and many other nations, governments have enacted a variety of laws designed to protect people from health dangers associated with secondhand smoke. Public interest and legislation to prevent smoking in workplaces and public buildings is on the rise as the public becomes more informed about the risks of secondhand smoke. The U.S. Surgeon General confirms that smoke-free workplaces are the only way to protect people from exposure to secondhand smoke in the workplace, since steps such as having separate smoking areas, air purification, and ventilating the building have all not been proven sufficient to prevent exposure if smoking is allowed inside the building.

What is Thirdhand Smoke?

Thirdhand smoke exposure is a new concept; it refers to the deposition and accumulation of toxic agents in smoke in clothing, drapes, rugs, furniture, dust, and other items due to secondhand smoke. These toxins can be absorbed through the skin and mucous membranes of non-smokers, especially by infants and young children.


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Medically reviewed by James E. Gerace, MD; American Board of Internal Medicine with subspecialty in Pulmonary Disease


"Secondhand smoke exposure: Effects in children"

"Secondhand smoke exposure: Effects in adults"

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