Winickoff says parents who try to protect their children from second-hand smoke by rolling down a window of the car or smoking only when the children are out of the room are not doing enough.

If the smell of the cigarette lingers, he said, so does the danger.

"You're nose isn't lying. If your body detects it, then it's there," he says.

"And children are more susceptible than adults."

third-hand smoke has been found to contain hydrogen cyanide, used in chemical weapons; butane; toluene, found in paint thinners; arsenic; lead; carbon monoxide; and polonium-210, the highly radioactive carcinogen that was used to murder former Russian spy Alexander V. Litvinenko in 2006.
—Stuart Laidlaw, "Toxins from 'third-hand smoke' linger on," The Toronto Star, January 6, 2009

That's 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 young children can get on their hands and ingest, especially if they're crawling or playing on the floor.

Doctors from MassGeneral 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 month's issue of the journal Pediatrics.
—Roni Caryn Rabin, "A New Cigarette Hazard: 'Third-Hand Smoke'," The New York Times, January 3, 2009

'What's that?' 'You can be victimized by third-hand smoke from being around people who smoke, even if they're not smoking, or who claim to be giving up smoking,' she explained. 'When such people speak or even breathe, they exhale dangerous toxins that, if inhaled, may be harmful and/or distasteful.
—Gerald Nachman, "When There's Smoking There's Ire," The San Francisco Chronicle, April 19, 1991