What is secondhand smoke?
Secondhand smoke is a byproduct of cigarette, cigar or pipe smoking. Secondhand smoke occurs when tobacco burns or when smokers exhale, and it is inhaled involuntarily by non-smokers.
Secondhand smoke is composed of two types of smoke. The first is called sidestream smoke, which is the smoke released from the burning end of a cigarette or cigar, or from tobacco burning in the bowl of a pipe. The second is called mainstream smoke, which is exhaled by a smoker.
Why is secondhand smoke dangerous?
When nonsmokers are exposed to secondhand smoke, they inhale many of the same cancer-causing chemicals that smokers inhale. According to the U.S. Surgeon General, cigarette smoke contains more than 4,000 chemical compounds, including more than 50 cancer-causing chemicals, and at least 250 chemicals that are either toxic or carcinogenic.
Both sidestream and mainstream smoke are dangerous to nonsmokers. For example, because sidestream smoke is generated at lower temperatures and under different conditions than mainstream smoke, it contains higher concentrations of many of the toxins found in cigarette smoke.
Secondhand smoke has been designated as a known human carcinogen by the U.S. Environmental Protection Agency, the National Toxicology Program, and the International Agency for Research on Cancer. Secondhand smoke also is listed as an occupational carcinogen by the National Institute for Occupational Safety and Health.
How can nonsmokers be protected from secondhand smoke?
According to the 2006 report by the U.S. Surgeon General, there is no risk-free level of exposure to secondhand smoke: even small amounts of secondhand smoke exposure can be harmful to people’s health.
A smoke-free environment is the only way to fully protect nonsmokers from the dangers of secondhand smoke. Separating smokers from nonsmokers, cleaning the air, and ventilating buildings can help, but they cannot eliminate the exposure of nonsmokers to secondhand smoke.