Help friends and relatives quit smoking, and learn how to clean third-hand smoke out of your home.

Where there's smoke, there are chemicals that linger for months.

RODALE NEWS, EMMAUS, PA—Smoking is responsible for one out of every five deaths every year, and exposure to secondhand smoke kills an additional 38,000 people every year, according to government statistics. But less is known about the risks of third-hand smoke, the chemicals left over from lingering tobacco that can stick around for months. A new study published in the Proceedings of the National Academy of Sciences has found that third-hand smoke mixes with common indoor air pollutants, and could be exposing the public to what the authors called an "unappreciated health hazard."

THE DETAILS: The researchers conducted lab tests in which they blew nicotine into chambers containing cellulose, a kind of fiber found in a number of fabrics, including cotton and rayon. They then exposed the material to nitrous acid, an indoor air pollutant that comes from gas appliances and vehicle exhaust, for three hours, at a level normally found inside homes. Their tests showed that the levels of cancer-causing chemicals called tobacco-specific nitrosamines (TSNAs) in the cellulose were 10 times higher after expousre to cigarette smoke and nitrous acid. Because nitrous acid comes from vehicle exhaust, they replicated their study in a pickup truck driven by a heavy smoker. They wiped surfaces to determine existing levels of TSNAs and then put a small amount of cellulose material inside the truck for three days, during which the driver smoked 34 cigarettes. The levels of TSNAs were roughly three times higher after the three days of smoke exposure than they were when the truck was first wiped down.

WHAT IT MEANS: Previous studies on the lingering chemicals from cigarette smoke, now called "third-hand smoke," have shown that cigarettes can leave behind as many as 250 different toxins. And the smoke carries them everywhere. "The burning of tobacco releases nicotine in the form of a vapor that adsorbs [attaches] strongly onto indoor surfaces, such as walls, floors, carpeting, drapes, and furniture," said this study's lead author Hugo Destaillats, PhD, a chemist with the Indoor Environment Department of Berkeley Lab's Environmental Energy Technologies Division, in a statement about his research. TSNAs, he warned, are "among the most broadly acting and potent carcinogens present in unburned tobacco and tobacco smoke."

Read on to learn how to get third-hand smoke out of your home.