What Is Thirdhand Smoke?

Even after they've been stubbed out, the effects of cigarettes can linger for years. Greentellect Studio/Shutterstock

Secondhand smoke, the cigarette smoke people breathe in when they're around people who are smoking, is recognized as a major cause of disease in nonsmokers, including lung cancer. Getting away from the smoke is obviously one way to avoid the ill effects, but it turns out that escaping the reach of cigarette smoke is remarkably difficult.

This is because the smoke and chemicals don't leave the room after the cigarette is put out or even after the room has been aired out. Instead, the funk becomes attached to surfaces and lingers, often for decades — meaning humans and animals can still be exposed to the harmful effects of cigarette smoke long after a cigarette has been discarded.

Call it thirdhand smoke.

Lingering effects

Thirdhand smoke hasn't garnered a lot of attention, but that's changing. Academic studies of its effects have increased over the past 10 years or so as we try to understand what it is and how we're being affected by it.

According to the Mayo Clinic, thirdhand smoke is the "residual nicotine and other chemicals left on indoor surfaces by tobacco smoke." Those surfaces are basically everything in the room when a cigarette was lit, including "clothes, furniture, drapes, walls, bedding, carpets, dust, vehicles and other surfaces." And just because smoking is limited to a single room doesn't mean it won't reach other surfaces around the space.

Getting rid of thirdhand smoke isn't easy. Simply airing out the room or running the air conditioning isn't enough to get the residue of the smoke out of surfaces. "To remove the residue," the Mayo Clinic writes, "hard surfaces, fabrics and upholstery need to be regularly cleaned or laundered." It may even be necessary to completely replace carpets and clean out ventilation systems.

Cigarette smoke wafts across curtains
Unless those curtains are cleaned thoroughly, that smoke is never really leaving the room. UzFoto/Shutterstock

Not doing so results in an environment that can cause smoking-related harm to animals and humans. Touching, inhaling or swallowing anything containing thirdhand smoke can cause the body to take in the residual chemicals. Because of this, babies — who are prone to touching and putting plenty of things into their mouths — are at a higher risk. Pets, because they're so close to carpets and rugs, are also likely to take in the thirdhand smoke quite easily.

Speaking to the Cleveland Clinic, pulmonologist Humberto Choi explains that thirdhand smoke can result in damage to DNA and lung cancer. Thirdhand smoke is becoming a potential suspect in lung cancer cases where no clear cause presents itself.

"There's been an increased interest recently because we are seeing more lung cancer cases that are not related directly to firsthand or secondhand smoking," Choi said. "So we're looking at other causes for cancer aside from direct exposure."

Thirdhand smoke spreads easily

Lest you think the case for thirdhand smoke is being overstated, consider a study published in Science Advances that tested the air quality of a college classroom in which smoking was prohibited and had been for at least 20 years. Smoking was also prohibited in the building.

Initially, researchers were curious about what happened to outdoor air particles as they came inside through a building HVAC system. However, when researchers used an aerosol mass spectrometer to measure the air composition of the classroom, which had not been used for a month, they kept finding the signatures of a chemical indoors that wasn't present outdoors. Indeed, the chemical made up 29 percent of the room's air mass. It turned out that this chemical was the residue of cigarette smoke, specifically thirdhand smoke.

But how did it get into the classroom in the first place?

Researchers pointed to two possible culprits. The first was an outdoor balcony about 65 feet away from the room. The balcony is a known hotbed of "illicit smoking activity." Thirdhand smoke could come in with the smokers after they had finished their cigarette.

The second potential culprit was a nearby office in the same HVAC zone as the classroom where several were several known smokers worked. Residual smoke and chemicals from their clothes may have been released into the air and circulated through the building by the HVAC system. You can learn more about how Pete DeCarlo of Drexel University and the other scientists involved in the study made their discoveries in the video below.