The Grapevine

What Is Thirdhand Smoking? Study Reveals How Tobacco Residue Can Spread Indoors

Most people are aware of the consequences of smoking tobacco, actively or passively. But a new study has drawn attention to a relatively lesser-known form of smoke exposure.

After measuring air composition with the help of an aerosol mass spectrometer, researchers found particles in the air of a non-smoking room contained chemicals from thirdhand smoke.

What is thirdhand smoke?

Thirdhand smoke (THS) refers to the residue of nicotine and other chemicals that linger in a room long after a cigarette is extinguished. This residue can remain on indoor surfaces such as clothing, carpets, walls, or furniture. While the dangers of secondhand smoke exposure led to the creation of smoke-free zones, THS remains a relatively new area of study with limited awareness among the general public.

Is THS harmful to human beings?

The health effects of THS have not been clearly understood. So far, only animal-based research has linked such smoke to asthma in mice in addition to lung cancer, insulin resistance, and liver problems.

Unlike secondhand smoke exposure, which occurs within a limited timeframe, people can be exposed to THS constantly, said Neal Benowitz, professor of medicine at the University of California. This makes it difficult to paint an accurate picture of its effects.

One study from 2016 suspected THS can form new carcinogens due to the interaction of nicotine and post-combustion tobacco constituents with other environmental chemicals.

What were the findings of the new study?

Researchers at Drexel University in Philadelphia measured the air composition inside a non-smoking classroom, finding that 29 percent of the indoor particulate matter was associated with the residue of THS.

A measurement took place once in August 2014 and another in August 2016, both yielding the same results. However, when the experiment was conducted during the winter season (when the room did not use air conditioning), they did not find THS compounds in the air. Thus, the researchers suspected these particles were delivered through the ventilation system.

The study titled "Thirdhand smoke uptake to aerosol particles in the indoor environment" was published in the journal Science Advances on May 9.

Who may be vulnerable to THS? How can we limit its exposure?

Experts suggested children, people with breathing problems, older adults, pregnant women, and animals were most at risk of suffering adverse effects. 

"I think children are the most vulnerable to thirdhand smoke because of exposure to surfaces like the floor and on their clothes and other objects in the house," said Dr. Humberto Choi, a pulmonologist from the Cleveland Clinic in Ohio. "If you smoke, never smoke inside your house, because even if you don't smell the smoke anymore, it's still there. Still, the best approach is to avoid it completely."

The American Academy of Pediatrics (AAP) also put forth recommendations for limiting and preventing THS exposure.