The health effects of involuntary smoking.

Involuntary smoking is defined as the exposure of nonsmokers to tobacco combustion products in the indoor environment. Involuntary smokers are exposed to a quantitatively smaller and qualitatively different smoke exposure than active smokers. Quantitation of exposure is particularly difficult in both physiologic and epidemiologic studies. Acute physiologic studies have documented minimal physiologic changes in healthy subjects. However, individuals with heart or lung disease may be differentially affected. A relatively large body of data relates parental (particularly maternal) cigarette smoking to the occurrence of both acute respiratory illnesses and chronic respiratory symptoms in children. The effect seems to be greatest early in life and cannot be separated from in utero exposure. Data linking parental smoking to lower levels of pulmonary function are all cross-sectional and less conclusive. What is apparent is that the magnitude of the direct effect of passive smoke exposure is likely to be relatively small (from 1 to 5% reduction in maximally obtained lung function level in exposed children). Data on adults are insufficient to allow for a quantitative estimate. The important effects of passive smoke exposure in childhood are twofold. The slight reduction in pulmonary function level may predispose individuals to increased risks from environmental agents later in life. In addition, having a parent who smokes substantially increases the likelihood that a child will become a smoker. Finally, two studies have linked lung cancer in nonsmokers to exposure to spouses' cigarette smoke. Further research is needed to confirm these findings. Involuntary smoking may have important health effects, either direct or indirect, which deserve further study.