Secondhand smoke is classified as a “known human carcinogen” (cancer-causing agent) by the US Environmental Protection Agency (EPA), the US National Toxicology Program, and the International Agency for Research on Cancer (IARC), a branch of the World Health Organization.
Tobacco smoke contains over 4,000 chemical compounds. More than 60 of these are known or suspected to cause cancer.
Secondhand smoke can cause harm in many ways. In the United States alone, each year it is responsible for:
* an estimated 46,000 deaths from heart disease in non-smokers who live with smokers
about 3,400 lung cancer deaths in non-smoking adults
* other breathing problems in non-smokers, including coughing, mucus, chest discomfort, and reduced lung function
* 150,000 to 300,000 lung infections (such as pneumonia and bronchitis) in children younger than 18 months of age, which result in 7,500 to 15,000 hospitalizations annually
increases in the number and severity of asthma attacks in about 200,000 to 1 million children who have asthma
* more than 750,000 middle ear infections in children
Pregnant women exposed to secondhand smoke are at increased risk of having low birth weight babies.
An issue that is still being studied is whether secondhand smoke may increase the risk of breast cancer. Both mainstream and secondhand smoke contain about 20 chemicals that, in high concentrations, cause breast cancer in rodents. And we know that in humans, chemicals from tobacco smoke reach breast tissue and are found in breast milk.
Any link between secondhand smoke and breast cancer risk in human studies is still being debated. This is partly because breast cancer risk has not been shown to be increased in active smokers. One possible explanation for this is that tobacco smoke may have different effects on breast cancer risk in smokers and in those who are exposed to secondhand smoke.
A report from the California Environmental Protection Agency in 2005 concluded that the evidence regarding secondhand smoke and breast cancer is “consistent with a causal association” in younger women. This means that the secondhand smoke acts like it could be a cause of breast cancer in these women. The 2006 US Surgeon General’s report, The Health Consequences of Involuntary Exposure to Tobacco Smoke, found that there is “suggestive but not sufficient” evidence of a link at this point. In any case, women should be told that this possible link to breast cancer is yet another reason to avoid being around secondhand smoke.
Secondhand smoke kills children and adults who don’t smoke, and makes others sick (Surgeon General’s report)
The 2006 US Surgeon General’s report reached some important conclusions:
Secondhand smoke causes premature death and disease in children and in adults who do not smoke.
Children exposed to secondhand smoke are at an increased risk of sudden infant death syndrome (SIDS), acute respiratory infections, ear problems, and more severe asthma. Smoking by parents causes breathing (respiratory) symptoms and slows lung growth in their children.
Secondhand smoke immediately affects the heart and blood circulation in a harmful way. Over a longer time it also causes heart disease and lung cancer.
The scientific evidence shows that there is no safe level of exposure to secondhand smoke.
Many millions of Americans, both children and adults, are still exposed to secondhand smoke in their homes and workplaces despite a great deal of progress in tobacco control.
The only way to fully protect non-smokers from exposure to secondhand smoke indoors is to prevent all smoking in that indoor space or building. Separating smokers from non-smokers, cleaning the air, and ventilating buildings cannot keep non-smokers from being exposed to secondhand smoke.
US Department of Health and Human Services