Third-hand smoke is what one smells when a smoker gets in an elevator after going outside for a cigarette, or in a hotel room where people were smoking. Your nose isn’t lying,” said Dr. Jonathan P. Winickoff, the lead author of the study and an assistant professor of pediatrics at Harvard Medical School. “The stuff is so toxic that your brain is telling you: Get away.”

Dr. Philip Landrigan, a pediatrician who heads the Children’s Environmental Health Center at Mount Sinai School of Medicine in New York, said the phrase third-hand smoke is a brand-new term that has implications for behavior.

“The central message here is that simply closing the kitchen door to take a smoke is not protecting the kids from the effects of that smoke,” he said. “There are carcinogens in this third-hand smoke, and they are a cancer risk for anybody of any age who comes into contact with them.”