Exposure to secondhand smoke can increase a baby's risk of respiratory problems, ear infections and sudden infant death syndrome. Ownby and his colleagues surveyed parents about their smoking habits and collected urine samples from 97 infants from birth to 2 years of age.
Researchers can find signs of smoke exposure by testing urine.
Although exposure to passive smoke was most highly correlated with the mothers' and fathers' smoking habits, it was also similarly correlated with the frequency of smoking by at-home day care providers, and by persons visited away from home, the authors report in the December issue of Archives of Pediatrics.