In 1996, the U.S. Centers for Disease Control and Prevention (CDC) found evidence of tobacco smoke exposure in the blood of 88 percent of American nonsmokers, via measurable levels of serum cotinine.

The presence of cotinine, a chemical the body metabolizes from nicotine, is documentation that a person has been exposed to tobacco smoke. Serum cotinine levels can be used to estimate nicotine exposure over the last 2 to 3 days.

Blood samples used in this study were taken from over 10,000 participants in the Third National Health and Nutrition Examination Survey (NHANES III) from 1988-1991. This survey, conducted by CDC’s National Center for Health Statistics, provides nationally representative data on the health status of the U. S. population through physical examinations and medical interviews.

Questionaire data from NHANES III on reported exposure to ETS show that 43 percent of U.S. children aged 2 months through 11 years lived in a home with at least one smoker, and that 37 percent of adult non-tobacco users lived in a home with a smoker or reported exposure to ETS at work.

Both the number of smokers in the household and the hours exposed at work were associated with increased serum cotinine levels. Data from NHANES III also revealed that the cotinine levels, and, therefore, exposure to second hand smoke was higher among children, non-Hispanic blacks, and males.

While this study itself did not address the health effects of environmental tobacco smoke, the 1993 report from the Environmental Protection Agency (EPA), a comprehensive analysis of many respiratory studies on the health effects of ETS, concluded that ETS caused lung cancer in adult non-smokers and serious respiratory problems in children.

Based on the health hazards of ETS, EPA has classified second-hand smoke as a Group A carcinogen (known to cause cancer in humans).