Secondhand Smoke

(updated September 2006)

Definition of Secondhand Smoke

  • Secondhand smoke, also known as environmental tobacco smoke, is a complex mixture of gases and particles that includes smoke from the burning cigarette, cigar, or pipe tip (sidestream smoke) and exhaled mainstream smoke.1
  • Secondhand smoke contains at least 250 chemicals known to be toxic, including more than 50 that can cause cancer.1

Health Effects of Secondhand Smoke Exposure

  • Secondhand smoke exposure causes heart disease and lung cancer in nonsmoking adults.2
  • Nonsmokers who are exposed to secondhand smoke at home or work increase their heart disease risk by 25–30% and their lung cancer risk by 20–30%.2
  • Breathing secondhand smoke has immediate harmful effects on the cardiovascular system that can increase the risk of heart attack. People who already have heart disease are at especially high risk.2
  • Secondhand smoke exposure causes respiratory symptoms in children and slows their lung growth.2
  • Secondhand smoke causes sudden infant death syndrome (SIDS), acute respiratory infections, ear problems, and more frequent and severe asthma attacks in children.2
  • There is no risk-free level of secondhand smoke exposure. Even brief exposure can be dangerous.2

Current Estimates of Secondhand Smoke Exposure

  • Exposure to nicotine and secondhand smoke is measured by testing the saliva, urine, or blood for the presence of a chemical called cotinine. Cotinine is a byproduct of nicotine metabolization, and tobacco is the only source of this marker.2
  • From 1988–91 to 2001–02, the proportion of nonsmokers with detectable levels cotinine was halved (from 88% to 43%).3
  • Over that same time period, cotinine levels in those who were exposed to secondhand smoke fell by 70%.3
  • More than 126 million nonsmoking Americans continue to be exposed to secondhand smoke in homes, vehicles, workplaces, and public places.2
  • Most exposure to tobacco smoke occurs in homes and workplaces.2
  • Almost 60% of U.S. children aged 3–11 years—or almost 22 million children—are exposed to secondhand smoke.2
  • About 25% of children aged 3–11 years live with at least one smoker, compared to only about 7% of nonsmoking adults.2
  • The California Environmental Protection Agency estimates that secondhand smoke exposure causes approximately 3,400 lung cancer deaths and 22,700–69,600 heart disease deaths annually among adult nonsmokers in the United States.4
  • Each year in the United States, secondhand smoke exposure is responsible for 150,000–300,000 new cases of bronchitis and pneumonia in children aged less than 18 months. This results in 7,500–15,000 hospitalizations, annually.5


   1. National Toxicology Program.   11th Report on Carcinogens, 2005.  (PDF–219KB) Research Triangle Park, NC: U.S. Department of Health and Human Sciences, National Institute of Environmental Health Sciences, 2000 [cited 2006 Sep 27]. Available from:
   2. U.S. Department of Health and Human Services. The Health Consequences of Involuntary Exposure to Tobacco Smoke: A Report of the Surgeon General. Atlanta, Georgia: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, Coordinating Center for Health Promotion, National Center for Chronic Disease Prevention and Health Promotion, Office on Smoking and Health, 2006 [cited 2006 Sep 27]. Available from:
   3. Pirkle JL, Bernert JT, Caudill SP, Sosnoff CS, Pechacek TF. Trends in the Exposure of Nonsmokers in the U.S. Population to Secondhand Smoke: 1988–2002. Environmental Health Perspectives. 2006;114(6):853–858 [cited 2006 Sep 27].
   4. California Environmental Protection Agency. Proposed Identification of Environmental Tobacco Smoke as a Toxic Air Contaminant. Final report, September 29, 2005, approved by Scientific Review Panel on June 24, 2005 [cited 2006 Sep 27]. Available from:
   5. United States Environmental Protection Agency. Respiratory Health Effects of Passive Smoking: Lung Cancer and Other Disorders.* Office of Research and Development, EPA/600/6-90/006F, Washington, D.C., December 1992 [cited 2006 Sep 27]. Available from:
      *Also published as: National Institutes of Health. National Cancer Institute. Respiratory Health Effects of Passive Smoking: Lung Cancer and Other Disorders: The Report of the U.S. Environmental Protection Agency. Smoking and Tobacco Control Monograph Number 4. NIH Publication No. 93-3605, Washington, D.C., August 1993.

For Further Information

Centers for Disease Control and Prevention
National Center for Chronic Disease Prevention and Health Promotion
Office on Smoking and Health
Phone: 1-800-CDC-INFO

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