So if you’re in a house or car where people smoke and you brush up against a wall, rug, or furniture, your skin could come into contact with dangerous chemicals. Third-hand smoke is especially risky for infants and toddlers, who are most likely to roll around on smoke soaked carpets. It’s not yet clear how potent smoke residue is, or how likely it is to cause diseases like cancer. But the study suggests that third-hand smoke may indeed pose a threat. And once smoke soaks into a surface, it’s usually there to stay. So unless you want smokey residue on your skin, it’s best to avoid places where people light up.