Although the prevalence of cigarette smoking has been steadily decreasing in the United States over recent years, 29 percent of adults and 30 percent of adolescents still currently smoke. As a consequence, the opportunity for infants and children to be exposed to environmental tobacco smoke (ETS) remains substantial, and the observed health effects attributed to such exposure will continue to be an issue for the foreseeable future. This review will summarize the current state of knowledge about the health effects of exposure to ETS in infants and children. Comprehensive reviews of the entire subject of involuntary smoking can be found in the recent reports of the Surgeon General of the United States and the report of the National Research Council. The known effects of direct maternal smoking on the outcomes of pregnancy and subsequent development of the infant are beyond the scope of this review and are well summarized elsewhere.
Environmental tobacco smoke is a combination of mainstream smoke (ms), the smoke inhaled by the smoker, and sidestream smoke (ss), the smoke that comes from the burning end of the cigarette. Sidestream smoke represents the major component of ETS. Although there are qualitative and quantitative differences between ms and ss, their overall compositions are similar. The central issue for health effects relates to quantitative differences in exposure between an active and an involuntary smoker, such as an infant or child. Factors such as the number of active smokers in a given environment and the size and ventilation characteristics of that environment further modify the exposure potential for the involuntary smoker.
Quantitative assessment of involuntary exposure of infants and children to ETS has been very imprecise and probably inaccurate. Most studies estimate exposure by questionnaire report of parental smoking without consideration of factors such as:
(1) the accuracy of the parental smoking history;
(2) the actual amount of time that a parent (or another individual) smokes in the presence of the infant/child;
(3) the intensity (number of cigarettes and smokers) of smoking at any given time; and
(4) the physical characteristics of the environment in which the smoking is occurring. Exposure outside the home environment is usually not considered.
The use of biologic markers, particularly of cotinine (a unique metabolic product of nicotine), has provided objective data that questionnaire reports of parental smoking and infant/child exposure to such smoking are accurate in terms of the dichotomy, “exposed”-“unexposed,” and, in some cases, in terms of magnitude of current exposure (eg, the number of cigarettes smoked by a mother). Unfortunately, this marker cannot provide objective verification of past exposure or cumulative exposure over the life of an infant/child.
Despite the limitations of the exposure data, the overall consistency in the findings of the studies of the health effects of exposure to ETS has made it possible to identify a series of potentially important health effects in infants and children that should be communicated by physicians to their patients.