Environmental tobacco smoke (ETS) is the combination of two forms of smoke from burning tobacco products:

• Sidestream smoke, or smoke that is emitted between the puffs of a burning cigarette, pipe, or cigar, and
• Mainstream smoke, or the smoke that is exhaled by the smoker. When a cigarette is smoked, about one-half of the smoke generated is sidestream smoke. This form of smoke contains essentially all of the same carcinogenic (cancer-causing) and toxic agents that have been identified in the mainstream smoke inhaled by the smoker, but at greater levels.

More than 4,000 individual compounds have been identified in tobacco and tobacco smoke. Among these are about 60 compounds that are carcinogens, tumor initiators (substances that can result in irreversible changes in normal cells), and tumor promoters (substances that can lead to tumor growth once cell changes begin). Some of these compounds are tar, carbon monoxide, hydrogen cyanide, phenols, ammonia, formaldehyde, benzene, nitrosamine, and nicotine.

The exposure of nonsmokers to ETS is referred to as involuntary smoking, passive smoking, and secondhand smoke. Nonsmokers who are exposed to ETS absorb nicotine and other compounds just as smokers do, and the greater the exposure to ETS, the greater the level of these harmful compounds in the body.

Although the smoke to which an involuntary smoker is exposed is less concentrated than that inhaled by smokers, research has demonstrated that the health risk from inhaling smoke is significant. For example, scientists estimate that ETS causes about 3,000 lung cancer deaths each year.

How Strong Is the Evidence Linking ETS With Lung Cancer?

In 1986, two reports were published on the association between ETS exposure and adverse health effects in nonsmokers: one by the U.S. Surgeon General and the other by the Expert Committee on Passive Smoking, National Academy of Sciences' National Research Council (NAS/NRC). Both of these reports concluded that:

• ETS can cause lung cancer in healthy adult nonsmokers;
• Children of parents who smoke have more respiratory symptoms and acute lower respiratory tract infections, as well as evidence of reduced lung function, than do children of nonsmoking parents; and
• Separating smokers and nonsmokers within the same air space may reduce but does not eliminate a nonsmoker's exposure to ETS.

More recent epidemiologic studies support and reinforce these earlier reports. The firmly established causal relationship between lung cancer and mainstream smoke, coupled with the chemical similarities between ETS and the smoke inhaled by smokers, led researchers to conclude that involuntary smoking is likely to have similar effects on the lung. In light of the widespread presence of ETS in both the home and workplace and its absorption by the body, the U.S. Environmental Protection Agency (EPA) released a report in 1992 in which ETS was classified as a Group A carcinogen a category reserved only for the most dangerous cancer-causing agents in humans.

The overall results of 30 epidemiologic studies of lung cancer and involuntary smoking further justify a Group A classification. In these studies, female never-smokers who are married to smokers are compared with female never- smokers who are married to nonsmokers. Higher exposures cause higher risks, and people whose spouses smoke in the home face a higher risk than that of people whose spouses do not smoke at home. In studies of ETS in the workplace, exposures are often even greater than exposure at home from spousal smoking.

While the EPA report focuses only on the respiratory health effects of involuntary smoking, there may be other health effects of concern as well. Recent studies suggest that ETS exposure also may be a risk factor for cardiovascular disease. In addition, a few studies link ETS exposure to types of cancer other than lung.

ETS Exposure in Infants and Children

Studies dating from the early 1970s have consistently shown that children and infants exposed to ETS in the home have significantly elevated rates of respiratory symptoms and respiratory tract infections. More than 50 recently published studies confirm these previous conclusions:

• ETS exposure due to parental smoking, especially the mother's, contributes to 150,000 to 300,000 cases annually of lower respiratory tract infection (pneumonia, bronchitis, and other infections) in infants and children under 18 months of age; 7,500 to 15,000 of these cases require hospitalization.
• ETS exposure is associated with increased respiratory irritation (cough, phlegm production, and wheezing) and middle ear infections, as well as upper respiratory tract symptoms (sore throats and colds) in infants and children.
• ETS exposure increases the number of episodes and the severity of asthma in children who already have the disease. The EPA report estimates that ETS worsens the condition in 200,000 to 1 million asthmatic children. Moreover, ETS exposure increases the number of new cases of asthma in children who have not previously exhibited symptoms.
• ETS exposure "in utero" and in infancy can alter lung function and structure and create other changes that are known to predispose children to long-term pulmonary risks.
• In the United States, sudden infant death syndrome (SIDS) is the major cause of death in infants between the ages of 1 month and 1 year, and the linkage with maternal smoking is well established. Current evidence strongly suggests that infants whose mothers smoke are at an increased risk of dying of SIDS. This risk is independent of other known risk factors for SIDS, including low birth weight and low gestational age, both of which are specifically associated with active smoking during pregnancy. Additional studies are needed to determine whether the increased risk is related to "in utero" or postnatal exposure to tobacco smoke, or to both.

These findings prompted recommendations that ETS be eliminated from the environment of small children. Thus, smoking should not be allowed in day care centers, nurseries, or other settings where infants and young children are cared for.

ETS Exposure in Nonsmokers with Existing Health Problems

ETS can worsen existing pulmonary symptoms in people with asthma and chronic bronchitis, as well as for people with allergic conditions. Even individuals who are not allergic can suffer eye irritation, sore throat, nausea, and hoarseness. Contact lens wearers can find tobacco smoke very irritating.

Public Policies Restricting Smoking

Following the release of the Surgeon General's report and the NAS/NRC review, many new laws, regulations, and ordinances were enacted that severely restrict or ban public smoking. With the release of the EPA report, many more such laws can be expected:

• On the Federal level, the General Services Administration issued regulations restricting smoking to designated areas only in Federal office buildings. Many agencies within the Public Health Service, which includes the National Institutes of Health, have banned smoking completely.
• By law, all airline flights of 6 hours or less within the United States and all interstate bus travel are smoke free.
• ETS meets the criteria of the Occupational Safety and Health Administration (OSHA) for classification as a potential occupational carcinogen. (OSHA is the Federal agency responsible for health and safety regulations in the workplace.)
• The National Institute for Occupational Safety and Health (NIOSH) is another Federal agency that is concerned with ETS exposure in the workplace. NIOSH conducts ETS-related research, evaluates worksites for possible health hazards, and makes safety recommendations. NIOSH recommends that ETS be regarded as a potential occupational carcinogen, in conformance with the OSHA carcinogen policy, and that exposures to ETS be reduced to the lowest possible levels.
• Currently, nearly every state has some form of legislation to protect nonsmokers; some states require private employers to enact policies that protect employees who do not smoke. In addition to state legislation, more than 560 local jurisdictions have enacted ordinances addressing nonsmokers' rights, and most are more restrictive than their state counterparts.

Additional Resources About the Effects of ETS

The NAS/NRC report "Environmental Tobacco Smoke: Measuring Exposures and Assessing Health Effects" (POD #318) is published by the National Academy Press. It may be ordered from the National Academy Press, Box 285, 2101 Constitution Avenue NW, Washington, DC 20055; the telephone number is 202-334-3313, and the toll-free number is 1-800-624-6242. The price is $58.25 plus $4.00 for shipping and handling per order. Orders must be prepaid by check or charged to VISA, MasterCard, or American Express.

"The Health Consequences of Involuntary Smoking: A Report of the Surgeon General" (stock number 017-001-00458-8) is available for $11.00 from the U.S. Government Printing Office, Post Office Box 371954, Pittsburgh, PA 15250-7954; the telephone number is 202-783-3238.

The EPA report "Respiratory Health Effects of Passive Smoking: Lung Cancer and Other Disorders" (stock number 055-000-00407-2) is available for $29.00 from the U.S. Government Printing Office, Post Office Box 371954, Pittsburgh, PA 15250-7954; the telephone number is 202-783-3238. The summary of this report and additional information on ETS are available free of charge from the U.S. Environmental Protection Agency, Indoor Air Quality, Post Office Box 37133, Washington, DC 20013-7133; the toll-free telephone number is 1-800-438-4318.

The NIOSH report "Current Intelligence Bulletin 54, Environmental Tobacco Smoke in the Workplace" is available from NIOSH's Office of Information, 4676 Columbia Parkway/ Mailstop C-19, Cincinnati, OH 45226. The toll-free telephone number is 1-800-35-NIOSH (1-800-356-4674).

The Office of Smoking and Health, Centers for Disease Control and Prevention, distributes materials on ETS. The Office can be contacted at 1600 Clifton Road, Rhodes Building/NE Mail Stop K-50, Atlanta, GA 30341-3724; the telephone number is 404-488-5705. The National Cancer Institute also publishes a free publication, "I Mind If You Smoke," which offers suggestions to nonsmokers about how to protect themselves from exposure to ETS at home, at work, and in public places.

Additional information on lung disease, cancer, and smoking is provided by the American Lung Association and the American Cancer Society. Local chapters of these organizations are listed in telephone directories.