It’s no secret that smoking cigarettes is (to put it mildly) bad for your health. And fewer of us, though still a substantial portion, understand that breathing in the smoke of someone else’s cigarette is nearly just as bad. The risks now go beyond that, one study argues, as the toxins left behind on surfaces and objects can grow deadly over time in what researchers call, “third-hand smoke.”

Anti-tobacco advocates often turn to the same general statistics in order to convince smokers to quit, and for good reason. Within 20 minutes of quitting, a person’s blood pressure and heart rate return to normal levels. Within a year, coronary heart disease risks are cut in half relative to a smoker. After 15 years, the risk of heart disease is back to that of a non-smoker. For as comforting as these stats may be, University of California, Riverside, researchers argue, smokers (and their families) aren’t in the clear. Long-term damage may still be done.

"We studied, on mice, the effects of third-hand smoke on several organ systems under conditions that simulated third-hand smoke exposure of humans," said Manuela Martins-Green, study leader and professor of cell biology at UC Riverside, in a statement. "We found significant damage occurs in the liver and lung. Wounds in these mice took longer to heal. Further, these mice displayed hyperactivity."

Lungs, Liver, Skin, And Brain

We all intuitively understand the effects of third-hand smoke. Smokers’ houses are notoriously yellowed, their carpets and drapes tinged with the after-effects of lingering smoke. The fact that furniture may stay tainted forever (or until it’s fumigated) should indicate the smoke’s lasting presence. But until Martins-Green and her colleagues did their current research, that data wasn’t available.

The team found damage in mice’s liver, lungs, and skin, along with impaired neurological function. Their livers showed elevated lipid levels and non-alcoholic fatty liver disease, a precursor to cirrhosis, cancer, and possibly cardiovascular disease. Mice’s lungs began producing excess collagen and several inflammatory agents, which have been linked to chronic obstructive pulmonary disease (COPD) and asthma. Mice with wounded skin showed slower healing, similar to humans after undergoing surgery. Their brains also showed hyperactivity — something the team saw as particularly troubling.

"The latter data, combined with emerging associated behavioral problems in children exposed to second- and third-hand smoke suggests that with prolonged exposure, they may be at significant risk for developing more severe neurological disorders,” Martins-Green explained.

According to the Centers for Disease Control and Prevention, tobacco use in the U.S. is at an all-time low. Roughly 19 percent of the adult population smokes, down from 42.4 percent in 1965, the earliest year the data is available. But the current study pokes something of a hole in that hopefulness, suggesting that a generation of heavy smokers may have raised their children, largely non-smokers, in an environment where, for all intents and purposes, they may as well have been smoking.

Putting Young Brains At Risk

Perhaps just as unsettling, third-hand smoke may also contribute to certain diseases associated with lifestyles that non-smokers don’t lead. "More recently we have found that exposure to third-hand smoke results in changes that can lead to type II diabetes even when the person is not obese," Martins-Green said. Children who grow up in houses of former smokers — and, worse, current smokers — also face a bevy of short-term and long-term health risks. This is to say nothing of the fact that children of smokers are twice as likely to begin smoking between age 13 and 21.

"There is still much to learn about the specific mechanisms by which cigarette smoke residues harm nonsmokers, but that there is such an effect is now clear,” Martins-Green said, adding that children who grow up in homes where secondhand and third-hand smoke are abundant miss 40 percent more days of school than children in nonsmoking homes.

According to the CDC, tobacco use remains the leading cause of preventable death in the United States. Among both male and female smokers, overall mortality rates are three times higher than those of people who have never smoked. And each year, some 440,000 people — or every one in five deaths — is the result of cigarette smoking.

Source: Martins-Green M, Adhami N, Frankos M. Cigarette Smoke Toxins Deposited on Surfaces: Implications for Human Health. PLoS One. 2014.