What is secondhand smoke?
Secondhand smoke refers to tobacco smoke that is passively breathed in by people in the vicinity of a person who is smoking. Terms that have been used to refer to secondhand smoke are passive smoking, involuntary smoking, or environmental tobacco smoke (ETS). 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).
When a nonsmoker inhales secondhand smoke, he or she is exposed to the same toxins and chemicals, including nicotine, as the smoker.
Exposure of children to secondhand smoke also increases their health risks; and children are especially vulnerable to the effects of environmental tobacco smoke. Even children who do not live with smokers may be at risk for adverse effects of secondhand smoke. Chemicals from tobacco smoke inhaled by a nursing mother are also known to reach breast milk.
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Secondhand Smoke Dangers
Secondhand smoke has many health risks for non-smokers including:
- lung cancer,
- heart disease,
- lung diseases (chronic cough, lung infections),
- asthma in children,
- middle ear infections,
- SIDS, and
- an increased risk of having a low-birthweight baby among pregnant women who are exposed to secondhand smoke.
What causes secondhand smoke?
Cigarettes are the most common sources of secondhand smoke, followed by cigars and pipe smoke. People can be exposed to environmental tobacco smoke anywhere - in their homes, in the workplace, and in recreational settings.
What are the health risks of secondhand smoke?
Secondhand smoke carries many health risks. At least 250 harmful chemicals have been identified in secondhand smoke, including at least 50 carcinogens (chemicals that are known to cause cancer). Just some of the dangerous chemicals present in secondhand smoke include vinyl chloride, cadmium, benzene, arsenic, and ethylene oxide.
Secondhand smoke is known to cause cancer. It has been classified as a "known human carcinogen" by the U.S. Environmental Protection Agency (EPA). It is also associated with cardiovascular and respiratory diseases as well as other serious health conditions; several are listed below.
Lung cancer and secondhand smoke
Passive smoking is an established risk factor for the development of lung cancer. Research has shown that nonsmokers who reside with a smoker have an increased risk for developing lung cancer when compared with nonsmokers who do not reside with a smoker.
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Other lung diseases and secondhand smoke
Coughing, chest congestion, and decreased lung function can also occur in those exposed to passive smoke. Babies exposed to secondhand smoke can also develop serious respiratory infections. Passive smoking is believed to cause lung infections (such as pneumonia and bronchitis) in children younger than 18 months of age each year.
Secondhand smoke and other effects on children
In addition to the risk of pneumonia and respiratory infections in babies exposed to secondhand smoke (see above), passive smoke is known to increase the severity of asthma in children with this condition. Middle ear infections in children are also occur as a result of exposure to secondhand smoke. Babies who are exposed to secondhand smoke are at an increased risk for sudden infant death syndrome (SIDS).
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Secondhand smoke and the effects on pregnant women
Like women who smoke, pregnant women who are exposed to secondhand smoke have an increased risk of having low-birthweight babies.
Secondhand smoke and the possible link to breast cancer
The question of whether or not passive smoking is associated with an increased risk of breast cancer is currently a source of both investigation and controversy. Breast cancer risk in active smokers is not known to be increased, yet some studies have found a possible link to breast cancer with exposure to passive smoke. In 2006, the U.S. Surgeon General's report concluded that there is "suggestive but not sufficient" evidence of a link at this point.
Is there a safe level of secondhand smoke?
While, logically, more extensive or prolonged exposure to secondhand smoke is associated with greatest risk of having medical problems as a result, no safe limit for exposure to secondhand smoke has been established. Even low levels of secondhand smoke can be harmful. This means that all exposure to secondhand smoke should be avoided whenever possible.
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What can be done about secondhand smoke exposure?
Local, state, and national governments have enacted a variety of laws designed to protect people from health dangers associated with secondhand smoke. These laws vary according to location. The American Lung Association has a listing of these regulations grouped by U.S. state (see References below). 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.
Obviously, quitting smoking if you are a smoker is the best way to protect your family and friends from secondhand smoke. A number of support systems, programs, and even prescription medications are available to help smokers break the habit.
If you are a non-smoker, the safest way to avoid passive smoke is not to allow others to smoke in your home. This is particularly important if there are children in your home. According to the U.S. Surgeon General, smoke-free workplaces are the only way to protect people from exposure to secondhand smoke in the workplace, since separate smoking areas, cleaning the air, and ventilating the building are not sufficient to prevent exposure if people still are permitted to smoke inside the building.
What is thirdhand smoke?
Thirdhand smoke exposure is a new concept; it is exposure to many of the toxic agents in smoke that have accumulated (as residue) in clothing, drapes, rugs, furniture, dust, and other items due to secondhand smoke. The toxic agents, deposited in and on items from secondhand smoke, can be absorbed through the skin and mucous membranes of non-smokers, especially by infants and young children. Prevention of secondhand smoke exposure can prevent thirdhand smoke exposure.
Medically Reviewed on 11/13/2018
Medically reviewed by William Fineman, MD; American Board of Internal Medicine with Subspecialty in Pulmonary Disease
American Cancer Society. "Secondhand Smoke."
American Lung Association. "Smoking restrictions in U.S. States."
National Cancer Institute. "Secondhand Smoke."
Sleiman, M., Gundel, L., Pankow, J., et al. "Formation of carcinogens indoors
by surface-mediated reactions of nicotine with nitrous acid, leading to
potential thirdhand smoke hazards." PNAS; doi:10.1073/pnas.0912820107