Secondhand Smoke: Questions and Answers


  • Secondhand smoke, also called environmental tobacco smoke, is the combination of smoke emitted from the burning end of a cigarette, cigar, or pipe, and smoke exhaled by the smoker.
  • Secondhand smoke contains at least 60 carcinogens.
  • The known health effects of exposure to secondhand smoke include lung cancer, nasal sinus cancer, respiratory tract infections, and heart disease.
  • Separating smokers and nonsmokers within the same air space may reduce, but does not eliminate, nonsmokers’ exposure to secondhand smoke.
  1. What is secondhand smoke?
  2. Secondhand smoke, also called environmental tobacco smoke, is the combination of two forms of smoke from burning tobacco products: sidestream smoke and mainstream smoke. Sidestream smoke, which makes up about half of all secondhand smoke, comes from the burning end of a cigarette, cigar, or pipe. Mainstream smoke is exhaled by the smoker. Exposure to secondhand smoke is also called involuntary smoking or passive smoking.

  3. What chemicals are present in secondhand smoke?
  4. 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. More than 4,000 chemicals have been identified in mainstream tobacco smoke; however, the actual number may be more than 100,000. Of the chemicals identified in secondhand smoke, at least 60 are carcinogens, such as formaldehyde. Six others are substances that interfere with normal cell development, such as nicotine and carbon monoxide.

    Some of the compounds present in secondhand smoke become carcinogenic only after they are activated by specific enzymes 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. In 1993, the U.S. Environmental Protection Agency determined that there is sufficient evidence that secondhand smoke causes cancer in humans and classified it as a Group A carcinogen. In 2000, the U.S. Department of Health and Human Services 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 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. 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.

  5. What are the health effects of exposure to secondhand smoke?
  6. Secondhand smoke exposure is a known risk factor for lung cancer. Approximately 3,000 lung cancer deaths occur each year among adult nonsmokers in the United States as a result of exposure to secondhand smoke. Secondhand smoke is also linked to nasal sinus cancer. Some research suggests an association between secondhand smoke and cancers of the cervix, breast, and bladder. However, more research is needed in order to confirm a link to these cancers.

    Secondhand smoke is also associated with the following noncancerous conditions:

    Certain other noncancerous health conditions may also be associated with secondhand smoke. However, more research is needed in order to confirm a link between these conditions and secondhand smoke. These conditions include:

  7. What is being done to reduce nonsmokers’ exposure to secondhand smoke?
  8. In January 2000, the DHHS launched Healthy People 2010, a comprehensive, nationwide health promotion and disease prevention agenda designed to help improve the health of all people in the United States during the first decade of the 21st century. Several objectives of this program relate to tobacco use and exposure to secondhand smoke, including the goal of reducing the proportion of nonsmokers exposed to secondhand smoke from 65 percent to 45 percent by 2010. More information about this program is available on the Healthy People 2010 Web site at on the Internet.

    Studies have shown that separating smokers and nonsmokers within the same air space may reduce, but not eliminate, nonsmokers’ exposure to secondhand smoke. Individuals can reduce their exposure to secondhand smoke by not allowing smoking in their home or car. Educational, clinical, and policy interventions have also been shown to reduce secondhand smoke exposure. Such policies include adoption of worksite restrictions, passage of clean indoor air laws, and enforcement of smoking restrictions in shared environments.

    On the national level, several laws restricting smoking in public places have been passed. For instance, effective January 1, 2005, smoking is banned in all DHHS buildings. In other Federal office buildings, smoking is limited to designated areas. Smoking is also banned on all domestic airline flights and nearly all flights between the United States and foreign destinations. All interstate bus travel is smoke free. Smoking is also prohibited or restricted to specially designated areas on trains traveling within the United States.

    Many states and local governments have passed laws prohibiting smoking in public facilities such as schools, hospitals, airports, and bus terminals. Some states also require private employers to create policies that protect employees who do not smoke, and several local communities have enacted nonsmokers’ rights laws, most of which are stricter than state laws. More information about state-level tobacco regulations is available through the Centers for Disease Control and Prevention’s State Tobacco Activities Tracking and Evaluating System Web site. The STATE System is a database containing up-to-date and historical state-level data on tobacco use prevention and control. This resource is available at on the Internet. Although it is still a significant public health concern, nonsmoker exposure to secondhand smoke declined by more than 70 percent from 1988–1991 to 1999–2000. In 1999, nearly 7 out of every 10 U.S. workers reported having a smoke-free policy in their workplace.

  9. Where can people find more information about research on secondhand smoke?
  10. The following resources provide additional information about secondhand smoke and its health effects:


      Environmental Protection Agency
      Ariel Rios Building
      1200 Pennsylvania Avenue, NW.
      Washington, DC 20460