Experts now have identified another smoking related threat to childrens health that isnt as easy to get rid of: third-hand smoke.

Thats the term being used to describe the invisible yet toxic brew of gases and particles clinging to smokers hair and clothing, not to mention cushions and carpeting, that lingers long after smoke has cleared from a room. The residue includes heavy metals, carcinogens and even radioactive materials that children can get on their hands and ingest, especially if theyre crawling or playing on the floor.

Doctors from Mass General Hospital for Children in Boston coined the term third-hand smoke to describe these chemicals in a new study that focused on the risks they pose to infants and children. The study was published in this months issue of the journal Pediatrics. Everyone knows that second-hand smoke is bad, but they dont know about this, said Dr Jonathan P Winickoff, the lead author of the study and an assistant professor of pediatrics at Harvard Medical School.

Third-hand smoke is what one smells when a smoker gets in an elevator after going outside for a cigarette, he said, or in a hotel room where people were smoking. Your nose isnt lying, he said. The stuff is so toxic that your brain is telling you: Get away.