Thirdhand Smoke Is the Most Difficult Kind to Avoid

It's invisible and it's everywhere smokers have been.

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Feb 20 2018, 6:00pm


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You don’t always need to see a lit cigarette to know if a place is smoker-friendly. You can smell it right away the moment you walk in—a faint, stale, musky tobacco odor that lingers long after the ashtrays have been emptied out.

The source of this smell is actually a type of residue known as thirdhand smoke, a combination of nicotine and other chemicals from tobacco that can accumulate over time, clinging to seat cushions, carpets, walls, even dust particles. And researchers are just beginning to understand the effects that it may be having on our health.

Unlike first and secondhand smoke, thirdhand smoke very literally sticks around, especially in smoker-friendly places like old casinos and bars. While the smoking bans that some states have put into place are a step in the right direction, they’re hardly an overnight fix: In a new study published this month, San Diego State University researcher Georg Matt found traces of thirdhand smoke in a California casino six months after the state instituted such a ban.

“We had expected high levels of thirdhand smoke early [on], but we were surprised by the massive amounts we found,” Matt says, adding that traces of nicotine and carcinogenic compounds remained high for several months following the ban.

By now, most people know the basics of first- and secondhand smoke: Willfully inhaling smoke—usually from a cigarette—is first-hand. Inhaling smoke you didn’t necessarily intend to inhale, such as when you walk past someone smoking on the street, is secondhand.

thirdhand smoke, however, is more insidious—it can be difficult to tell exactly which surfaces are contaminated, and how much. It’s possible most people don’t even know they’re being affected. One reason is that nicotine can combine with ozone molecules to create potentially dangerous compounds known as tobacco-specific nitrosamines, says Manuela Martin-Green, professor and chair of the department of molecular, cell, and systems biology at the University of California. In both children and adults, these compounds can be absorbed through the skin, resulting in carcinogens entering the body.


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Research has already shown that children and people with compromised immune systems are especially prone to complications as a risk of exposure. In one small study that looked at five newborn babies of mothers who smoked, for instance, researchers found traces of nicotine on the babies’ incubators. Nicotine metabolites also showed up in the newborns’ urine samples. (secondhand smoke was not a factor since the study was conducted in the hospital’s NICU.)

While it’s not yet clear how serious the long-term effects of this exposure are, early research on human cells has already linked thirdhand smoke to genetic damage. In rodent studies, neonatal mice exposed to thirdhand smoke over a period of several weeks weighed significantly less than mice in a control group. They also showed lower levels of white blood cells, which help the body fight infection. Other mouse studies have suggested that exposure to thirdhand smoke could lead to insulin resistance, a precursor to type-2 diabetes.

Unlike first- and secondhand smoke, thirdhand smoke is also highly persistent—avoiding it isn’t as simple as quitting the habit or walking away. If heavy smokers have recently shared the space you’re occupying—such as a hotel room or a rental car—odds are there’s thirdhand smoke present.

Worse, there’s no easy way to get rid of thirdhand smoke—or to feel secure in the fact that it’s truly gone. Depending on the extent of the pollution, removal may require merely cleaning—washing and vacuuming—or it may require removing carpets, furniture, and wall boards, Matt says. “Painting walls can temporarily trap surface-bound thirdhand smoke,” he says, “but it cannot permanently seal walls and prevent volatile compounds that penetrated into the drywall from off-gassing.”

As preventative measures go, appliances such as air purifiers don’t always help, either. “Some simply cover up odors such that the human nose can no longer identify a smelly compound,” Matt says. “Others cause a chemical reaction that transforms a odorant compound into odorless compounds. Unfortunately, some of these chemical reactions just produce new toxic compounds.”

Risk, however, is correlated with your level of exposure—the less time you spend around contaminated surfaces, the lower your likelihood of being affected. Matt advises people to avoid chronic exposure—which means you should avoid buying a home or renting an apartment if it was previously occupied by heavy smokers. “This is especially true for vulnerable and sensitive populations—infants and children, people with asthma, and people who are immune compromised,” he says.

In the meantime, until more sophisticated methods of detection are developed, it helps to simply use the most primitive one we have. “If you can smell it,” Martin-Green says, “thirdhand smoke is around.”

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