You previously warned that triclosan, an ingredient in antibacterial soaps, produces a carcinogenic chemical when it reacts with chlorine in tap water. Do toothpastes containing triclosan present a cancer danger? —R.M., New York City

It seems unlikely. Pilot studies raising that cancer concern looked at soaps containing triclosan, not toothpastes. Evidence suggests that even with soaps, the amount of the carcinogen released is comparable to that normally found in some tap water. And the reactions documented in the most recent, widely publicized soap study require much more chlorinated water than you’d come in contact with when brushing your teeth. Triclosan in toothpaste thus isn’t likely to be a concern, according to the study’s author. The American Dental Association has also stated that a warning about the potential harm from soaps containing triclosan doesn’t apply to toothpaste.