Secondhand Smoke Increases Breast Cancer Risk


Women who are exposed to secondhand smoke for a long time and at high levels may be at increased risk of developing breast cancer, even if they never smoked cigarettes themselves. Results of the new study appear in Cancer Epidemiology, Biomarkers & Prevention.

Secondhand smoke has been classified as a “known human carcinogen” by the US Environmental Protection Agency (EPA), the US National Toxicology Program, and the International Agency for Research on Cancer. Tobacco smoke contains more than 4,000 chemical compounds, of which more than 60 are known or suspected carcinogens.

Research has already revealed that secondhand smoke is responsible for a variety of health problems, according to the American Cancer Society. For example, it is linked to about 46,000 deaths from heart disease in non-smokers who live with smokers, about 3,400 lung cancer deaths in non-smoking adults, 150,000 to 300,000 lung infections in children younger than 18 months of age, and an increased risk of delivering a low birth-weight baby or having fertility problems. It’s also been shown that secondhand smoke contains about 20 chemicals that, in high concentrations, cause breast cancer in rodents.


In the current study, researchers collected information via questionnaire from more than 57,000 women in the California Teachers Study and followed them for ten years. The investigators evaluated the risk of developing breast cancer among women who had no history of breast cancer and who had never smoked tobacco products but who had been exposed to secondhand smoke in various settings.

A total of 1,754 newly diagnosed cases of invasive breast cancer occurred since the women completed the questionnaire. The researchers found that while exposure to secondhand smoke before age 20 did not appear to increase the risk of breast cancer, the combination of exposure to moderate to high levels for a long period of time did increase the risk. The results of this study add to the list of health risks associated with exposure to secondhand smoke.


American Association for Cancer Research
American Cancer Society