• Factors affecting exposure and the assessment of exposure. To what extent is the nonsmoker exposed to harmful chemicals that can be measured in ETS? How can we measure exposure to ETS? Can ambient monitoring be used in epidemiological studies? How reliable is questionnaire information? What constitutes the dose a person may receive? Are there objective measures of dose received, such as tobacco-smoke-specific biological markers? What choices and reasons for choice are there among the markers?

• Effects of exposure. What are the health effects, if any, consequent to exposure to ETS? Are these health effects related to discomfort or irritant effects only, or more serious disease? Are the potential health effects reversible when exposure ceases? What are the data from human studies? Do interactions with other environmental agents at workplaces or in homes need to be considered? Are there biologically plausible explanations for the various effects ascribed to ETS exposure?

The report considers sensitive populations such as children, pregnant women, older persons, and those with persisting respiratory illnesses. It does not consider the established effects on the fetus carried by a pregnant, smoking woman because this is not an instance in which a nonsmoking individual breathes ETS generated by other people. However, a pregnant, nonsmoking woman might be affected by exposure to ETS, as may her fetus.

The health effects considered include respiratory symptoms and lung function, and other respiratory ailments (especially in children), such as asthma and allergic responses, cancer at various sites, and cardiovascular disease, among others. Some attention is paid to irritation, annoyance, and associated responses.

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