A woman smokes in Chile in this March 14, 2006 file photo. (Xinhua/Reuters Photo)

You've perhaps known about the harmful effects of secondhand smoke, but experts warn that third-hand smoke is also dangerous, according to a study in the Pediatrics quoted by media on Tuesday.

Third-hand smoke is the residual contamination from tobacco smoke that remains after a cigarette is put out. Researchers say it's a toxic dust that settles onto surfaces and can spread in the air.

The study was conducted by the Massachusetts General researchers.

"Children are especially susceptible to third-hand smoke exposure because they breathe near, crawl and play on, touch and mouth contaminated surfaces," according to the study.

The residue found in third-hand smoke includes heavy metals, carcinogens and, even radioactive materials that are dangerous to children.

Joel Africk, president and CEO of the Respiratory Health Association of Metropolitan Chicago, said that the Pediatrics study does not call for legislation that would ban smoking in private homes instead serving as a reminder to all smokers and non-smokers.

(Xinhua News Agency via Agencies January 6, 2009)