The nicotine in smoke that adheres to surfaces like foors, curtains, furniture and wall reacts with common indoor air pollutant to create dangerous carcinogens.

That's according to a study by several institutes led by the Lawrence Berkeley National Laboratory.

Berkeley Lab chemists Lara Gundel and Hugo Destaillats led a research team that revealed the potential health hazards posed by residual nicotine in third-hand smokeHugo Destaillats, a chemist with Berkley Lab's Environmental Energy Technologies Division said that nicotine from smoking is released as a vapour that adsorbs onto carpets and the rest and can stay there for days, weeks and months. "When this residual nicotine reacts with ambient nitrous acid it forms carcinogenic tobacco specific nitrosamines or TSNAs," he said.

He is the author of a paper in The Proceedings of the National Academy of Sciences, along with Mohamad Sleiman, Lara Gundel and Brett Singer.

Unvented gas appliances are the main source of nitrous acid inside homes. The study said third hand smoke "would seem to pose the greatest hazard to infants and toddlers". Opening a window or using a fan while smoking a fag won't eliminate the hazard. And even smoking outside doesn't help much, apparently.

"Smoking outside is better than smoking indoors but nicotine residues will stick to a smoker's skin and clothing. Those residues follow a smoker back inside and get spread everywhere."