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What chemicals are present in secondhand smoke?

Many factors affect what chemicals are present in secondhand smoke
These factors include the type of tobacco, the chemicals added to the tobacco, how the product is smoked, and the paper in which the tobacco is wrapped (10, 12). More than 4,000 chemicals have been identified in mainstream tobacco smoke; however, the actual number may be more than 100,000 (10). Of the chemicals identified in secondhand smoke, more than 50 are carcinogens (substances that cause cancer), such as formaldehyde . Six other substances, including nicotine and carbon monoxide, interfere with normal cell development (11, 13). Some of the compounds present in secondhand smoke become carcinogenic only after they are activated by specific enzymes ( proteins that control chemical reactions) in the body. After these compounds are activated, they can then become part of a cell’s DNA and may interfere with the normal growth of cells (14). In 1993, the U.S. Environmental Protection Agency (EPA) determined that there is sufficient evidence that secondhand smoke causes cancer in humans and classified it as a Group A carcinogen (11, 15). In 2000, the U.S. Department of Health and Human Services (DHHS) formally listed secondhand smoke as a known human carcinogen in The U.S. National Toxicology Program’s 10th Report on Carcinogens. The most recent report can be found at http://ntp.niehs.nih.gov/ntp/roc/toc11.html on the Internet.   Scientists do not know what amount of exposure to secondhand smoke, if any, is safe. Because it is a complex mixture of chemicals, measuring secondhand smoke exposure is difficult and is usually determined by testing blood , saliva , or urine for the presence of nicotine, particles inhaled from indoor air, or cotinine (the primary product resulting from the breakdown of nicotine in the body) (10, 12). Nicotine, carbon monoxide, and other evidence of secondhand smoke exposure have been found in the body fluids of nonsmokers exposed to secondhand smoke. Nonsmokers who live with smokers in homes where smoking is allowed are at the greatest risk for suffering the negative health effects of secondhand smoke exposure (14).