The dangers of smoking are well-known. Inhaling nicotine and other toxic chemicals in cigarette smoke, either firsthand as a smoker or secondhand as a non-smoker, may cause illnesses like heart disease, stroke and lung cancer. What isn’t as clearly understood is the effect of so-called “thirdhand smoke,” a term coined to describe the potentially cancer-causing compounds that form when tobacco smoke particles mix with gases in the air, absorbing into nearby surfaces, like carpets, rugs, clothes, bedsheets, wall paint, car dashboards, and even toys. The residue from tobacco smoke may remain in these materials for years after a burning cigarette is extinguished, and many researchers worry it may be harmful to people’s health. But determining the risk from thirdhand smoke is difficult, and data on its effects are still scarce.
"People hear about the dangers of smoking. They hear about the dangers of secondhand smoke. But they don't hear much, if anything, about the dangers of thirdhand smoke. What's tricky about thirdhand smoke is that you can't really quantify the risk."
— Rabih Bechara, MD, FCCP - Chief of Interventional Pulmonology, Pulmonary and Critical Care Medicine at our hospital in Atlanta
Thirdhand smoke forms when particles from a cigarette or other tobacco-burning device seep into materials like hair, clothes, furniture, carpet and walls, and are absorbed. The chemicals then undergo an aging process, which changes their chemical structure. Nicotine reacts with indoor air pollutants like nitrous acid to form carcinogens, or compounds that may cause cancer. The gas is then continuously re-emitted back into the air in a process called “off-gassing.”
Efforts to diffuse the smoke, like opening windows or using a fan, don’t prevent thirdhand smoke from forming or keep it from being inhaled, and the residue may give off harmful chemicals for years or even decades. “Thirdhand smoke is not a one-time thing,” Dr. Bechara says. “It’s actually a phenomenon that accumulates over time with increased exposure.” Normal cleaning methods also aren’t effective against the pollutants. Most of the time, replacing carpets or repainting walls are the only options.
Although it’s a relatively new term, thirdhand smoke has been a research topic for decades. It was first discovered in 1953, when a scientist from the Washington University School of Medicine in St. Louis found that tobacco smoke condensate—or liquid from gas condensation—painted on mice caused cancer. In a 1991 study, researchers found nicotine in the dust of smokers’ homes. A later study, conducted in 2004, found that nicotine was still present in homes where smokers tried to limit exposure, such as smoking outdoors. A 2008 study comparing the cars of smokers to non-smokers’ vehicles showed similar results, even finding that the dashboards of cars driven by smokers who banned smoking in their vehicles had tobacco residue.
The term “thirdhand smoke” became widely known when it was used in a 2009 paper published in Pediatrics. In it, the authors theorized that stressing the potential dangers of thirdhand smoke to children’s health could help persuade adults to quit the habit: “Children are especially susceptible to thirdhand smoke exposure because they breathe near, crawl and play on, touch, and mouth contaminated surfaces.” To reduce the risk to children, the American Academy of Pediatricians issued recommendations to limit children’s exposure. “This is something that’s very important for smokers to know about because it could be an incentive for them to quit smoking for the sake of themselves and their loved ones,” Dr. Bechara says. “Awareness of thirdhand smoke can help smokers realize that it’s not just themselves they’re potentially harming.”
Although no research has been conducted yet on the effects of thirdhand smoke on humans, studies have shown that mice exposed to thirdhand smoke have a greater chance of developing lung cancer. “The important thing to know is that there is a risk, and this risk could predispose people to certain health issues, including lung cancer, liver damage and diabetes,” Dr. Bechara says.
