Definitions

Environmental tobacco smoke (ETS) originates from the smoldering end of the tobacco product in between puffs, known as sidestream smoke (SS), and from the smoker's exhaled smoke. [The smoke that the smoker inhales is known as mainstream smoke (MS).] Other contributors to ETS include minor amounts of smoke that escape during the puff-drawing from the burning cone and some vapor-phase components that diffuse through the cigarette paper into the environment. These various components are released into the environment and are diluted by ambient air. They may also aggregate with pollutants already in the environment and thereby change character. The composition of this complex mixture, known as ETS, has different physicochemical characteristics than the MS.

There are various terms in the literature that refer to the inhalation of ETS by nonsmokers, e.g., "passive smoking," "involuntary smoking," and "breathing other people's smoke.'' We will refer to the inhalation of ETS by using the terms "passive smoking" and "exposure to ETS by nonsmokers'' interchangeably.

Trends in Cigarette Usage

Exposure of nonsmokers to ETS is a function of several variables, one of which is the number of active smokers with whom the nonsmoker comes into contact throughout some period of time. The percent of the population who smoke steadily increased over the first two-thirds of this century but has declined more recently. In 1980, 32% of the adult population considered themselves to be cigarette smokers (U.S. Department of Commerce, 1984). This percentage, now roughly equal for men and for women, reflects a reduction of almost one-third in men since the publication of the first Surgeon General's Report on Smoking and Health in 1964 (U.S. Public Health Service, 1964). Figure 1-1 shows the trends in cigarette usage between 1955 and 1985 for males and females. Table 1-1 gives cigarette consumption since 1900. Table 1-2 illustrates an overall increase in cigar and pipe smoking, followed by a decline during the past decade. The actual probability of exposure to ETS is complex, affected by ventilation rates, size of houses, restrictions on where tobacco products may be smoked, and changes in the cigarette itself. The consequence of Figure 1-1 is that the general probability of being exposed to some ETS for the nonsmoker has increased until quite recently.

Figure 1-1

Percentage of current smokers in the United States. Adult population, By sex, 1955-1953. From Shopland and Brown (1955).

TABLE 1-1

U.S. Cigarette Consumption, 1900 to 1985.

TABLE 1-2

U.S. Consumption of Cigars and Tobacco for Pipes and Hand-rolled Cigarettes.

The magnitude of exposure to ETS will depend upon the number of cigarettes and/or cigars and pipes smoked in a given environment, as well as other factors such as ventilation. Light smokers are more likely to stop smoking than heavy smokers, which might explain why over the past 30 years the number of cigarettes per smoker and the total consumption (Figure 1-2) have not declined as rapidly as the percentage of people who smoke (see also cigar and loose tobacco consumption in Table 1-2). From a peak consumption in the early 1960s, there has been a decline of 20% in the per capita (U.S.) consumption of cigarettes (Shopland and Brown, 1985). These data, however, are averaged over the total U.S. population, including smokers and nonsmokers. Among persons who consider themselves smokers, the cigarette consumption per adult smoker actually has increased from 27.3 to 30.0 cigarettes per clay. Table 1-3 demonstrates that, for both sexes, the percent of smokers who are heavy smokers has steadily increased over the past 30 years. Therefore, the consumption per active smoker indicates that the nonsmoker who has close contact with a smoker may be exposed to greater amounts of smoke in 1985 than in 1955, although the total number of hours a nonsmoker is exposed to ETS would have declined.

Figure 1-2

Total cigarette consumption (domestic sales), 1955- 1985.

TABLE 1-3

Number of Cigarettes Smoked per Day, as a Percentage of Current Smokers, by Sex.

Counteracting this trend of increased exposure has been the trend of reduction in amount of tobacco used to fill each cigarette. Physical changes of the leaf due to modern methods of processing, the use of filter tips (United States, >90% of all cigarettes since 1978; Griese, 1984), and variations in the composition of tobacco blends for cigarettes (Norman, 1982) have made this reduction possible.

In 1956, the U.S. average tar and nicotine yields were 38.4 mg and 2.69 rag, respectively. Since then, tar and nicotine yields have steadily decreased to 13.2 mg tar and 0.95 mg nicotine in 1980 (The Tobacco Institute, 1981). However, tar and nicotine yields in the SS of cigarettes have not significantly changed except in the case of cigarettes designed for ultralow yields of tar and nicotine. Certain other components, in particular volatile, toxic components, are released into SS in significantly greater amounts than into MS. Furthermore, ETS contains significantly smaller particles than MS, and nicotine, and perhaps other smoke constituents, is volatilized to a greater extent in SS than in MS. This means that the gas-phase composition of SS differs substantially from that of MS.

The health implications to nonsmokers of exposure to ETS may not be a simple extrapolation from the studies of active smokers. The complexities of such extrapolations will be discussed.

Children represent a large population of nonsmokers who may be exposed to environmental smoke. Several cohort studies of children are reviewed in Chapter 11. Although there is some variation among these studies, they indicate, mainly through questionnaires, that between 50 and 65 percent of the children have been exposed to tobacco smoke in the home during the past 20 years. Health implications of this exposure for the developing child will be discussed.

Organization

This report begins with a discussion of the components of ETS (Chapter 2) and what in vivo and in vitro studies have determined about ETS (Chapter 3). Various methods of exposure assessment are considered in Chapters 4 through 8, including physical effects, questionnaires, and biological markers. Chapters 9 through 15 review epidemiologic studies of possible health effects of these exposures. The health consequences examined range from irritation and allergic reactions to cancer and cardiovascular disease. Only studies that assess exposures under experimental conditions or in the home are included. ETS potentially interacts with constituents of the ambient air. This makes the evaluation of possible health effects due to workplace exposure complex and specific to each situation because of the varying nature of contaminants. Each chapter concludes with a summary of what is currently known, the strength of that knowledge, and what additional information would further clarify the relationship of ETS and possible health effects. Some recommendations for additional research are also given.

References

• Griese, V.N. Market growth of reduced tar cigarettes. Recent Adv. Tob. Sci. 10:4-14, 1984.
• Lee, P.N., editor. , Ed. Tobacco Consumption in Various Countries, pp.82-84. London, England: Tobacco Research Council, 1975.
• National Research Council, Committee on Airliner Cabin Air Quality. Airliner Cabin Environment: Air Quality and Safety. Washington, D.C.: National Academy Press, 1986. 303 pp.
• Norman, V. Changes in smoke chemistry of modern day cigarettes. Recent Adv. Tob. Sci. 8:141-177, 1982.
• Shopland, D.R., and C. Brown. Changes in cigarette smoking prevalence in the U.S.: 1955-1983. Ann. Behav. Med. 7:5-8, 1985.
• The Tobacco Institute. U.S. tar/nicotine levels dropping. The Tob. Observ. 6:1, 1981.
• Tobacco Reporter. Cigars in the U.S.: Is the upturn real? Tob. Rep. 111:43-46, 1984.
• U.S. Department of Agriculture. Tobacco: Outlook and Situation Report. DOA Publ. No. TS-129. Washington, D.C.: U.S. Government Printing Office, 1985.
• U.S. Department of Commerce. Statistical Abstract of the United States: 1985. Washington, D.C.: U.S. Department of Commerce, Bureau of the Census, 1984. 119 pp.