Secondhand smoke is a mixture of the smoke given off by the burning end of a cigarette, pipe, or cigar, and the smoke exhaled by smokers. Secondhand smoke is also called environmental tobacco smoke (ETS) and exposure to secondhand smoke is sometimes called involuntary or passive smoking. Secondhand smoke contains more that 4,000 substances, more than 40 of which are known to cause cancer in humans or animals.
EPA has concluded that exposure to secondhand smoke can cause lung cancer in adults who do not smoke. EPA estimates that exposure to secondhand smoke causes approximately 3,000 lung cancer deaths per year in nonsmokers.
Exposure to secondhand smoke has also been shown in a number of studies to increase the risk of heart disease.
Breathing secondhand smoke can be harmful to children's health including asthma, Sudden Infant Death Syndrome (SIDS), bronchitis and pneumonia and ear infections. Children's exposure to secondhand smoke is responsible for: (1) increases in the number of asthma attacks and severity of symptoms in 200,000 to 1 million children with asthma; (2) between 150,000 and 300,000 lower respiratory tract infections (for children under 18 months of age); and, (3) respiratory tract infections resulting in 7,500 to 15,000 hospitalizations each year.
The developing lungs of young children are severely affected by exposure to secondhand smoke for several reasons including that children are still developing physically, have higher breathing rates than adults, and have little control over their indoor environments. Children receiving high doses of secondhand smoke, such as those with smoking mothers, run the greatest risk of damaging health effects.
Source: Respiratory Health Effects of Passive Smoking (Also Known as Exposure to Secondhand Smoke or Environmental Tobacco Smoke - ETS) (U.S. Environmental Protection Agency, 1992)
In adults, ETS is a human lung carcinogen, responsible for approximately 3,000 lung cancer deaths annually in U.S. nonsmokers. ETS has been classified as a Group A carcinogen under EPA's carcinogen assessment guidelines. This classification is reserved for those compounds or mixtures which have been shown to cause cancer in humans, based on studies in human populations.