The study, funded by the National Institutes of Health, analyzed data from the Family Life Project, an ongoing longitudinal study of poor families in six rural counties of Pennsylvania and North Carolina who added a child between September 2003 and August 2004. Researchers measured levels of cotinine, which the body makes from nicotine, in the saliva of 1,218 children at ages 6,15, 24, and 48 months; about 63 percent had detectable levels, and about 12 percent had at least as much as one would expect to find in an active adult smoker.
"Greater exposure was associated with lower income, less education, more residential instability, and more instability in adult occupants in the home, whereas time spent in center-based day care was associated with lower exposure," the researchers write.
Greater residential instability correlates with higher smoke exposure because thirdhand smoke lingers, so a nonsmoking family that moves into a home once occupied by a smoker will likely be exposed to thirdhand smoke. Poverty is associated with frequent moves, which the researchers hypothesize could increase such children's risk of thirdhand smoke exposure. More time in a center-based daycare lowers the risks of smoke exposure; day-care centers are generally smoke-free.