Infants and Second Hand Smoke
Nearly half the infants exposed to second-hand smoke from their parents' cigarettes showed signs of a potent carcinogen in their urine, according to this study
. The carcinogen substance in question, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, or NNK, is known to cause cancer in rats. It is also the most likely cancer-causing agent in active or passive smokers.