Second-hand smoke is a term that generally refers to inhaling tobacco smoke coming from someone else’s burning cigarette or smoke that has been exhaled.

Many people are shocked to learn that, according to the American Cancer Society, this kind of smoke can have even higher concentrations of carcinogens (cancer-causing agents) than smoke inhaled directly by the smoker.

Third-hand smoke, on the other hand, is a relatively new concept. Third-hand smoke refers to the residue of nicotine and other chemicals that is left behind on surfaces after coming in contact with tobacco smoke. People can be exposed to third-hand smoke by touching surfaces contaminated with it. Researchers are still studying its possible dangers.

“This residue is thought to react with common indoor pollutants,” says Dr. Lowell Dale with the Mayo Clinic. “This toxic mix . . . poses a potential health hazard to nonsmokers exposed to it, especially children.”

According to Dale, third-hand smoke typically clings to clothes, furniture, upholstery, and carpets. Because it clings to surfaces, it cannot be removed by simply airing out rooms.

Over time, “It [can] build up on surfaces and can even resist normal cleaning,” adds Dale.

“This is a big concern for hotels that allow guest room smoking,” says Mark Baxter, an engineer with U.S. Products. “Small children may crawl on carpets coated with third-hand smoke, essentially putting themselves at risk for cross contamination with third-hand smoke.”

While Dale says the best way to protect nonsmokers from this risk is to create smoke-free environments, Baxter believes there are steps cleaning professionals can take to address the problem in homes and commercial facilities.

“Removing third-hand smoke from carpets calls for restorative cleaning,” he says. “Select effective chemicals. If pre-spraying carpets, make sure the chemical is allowed proper ‘wet’ dwell time. And use extractors that heat the water/cleaning solution. Heat makes the entire cleaning process more effective.”