A smoker steps outside to have a quick cigarette. They wait to light up until they’re well beyond the state-mandated smoke-free area outside the building’s door. No one is around. When they’re done, they put out the butt, dispose of it properly, and walk back inside.

As far as current laws and social norms go, this smoker has done everything right. But new research published Wednesday in Science Advances reports that even these best-intentioned smokers could have negative effects on those around them — thanks to the toxic chemicals that linger on their clothes and are brought indoors.

Thirdhand Smoke

While smokers, of course, experience smoke firsthand, those in the direct presence of a lit cigarette are exposed to secondhand smoke. Now, researchers are bringing attention to a new type of exposure: thirdhand smoke.

Thirdhand smoke is the residual contamination of surfaces and spaces with nicotine and other chemicals from smokers, which others breathe in through dust or gases. And unlike secondhand smoke, thirdhand smoke is unseen and can often go unnoticed.

In the new study, researchers from Yale University and the Max Planck Institute for Chemistry looked to a well-ventilated movie theater where smoking had been banned for 15 years. Over four days, the team measured the air in the theater before moviegoers arrived, as well as throughout the movie.

At the Movies

The researchers found that toxic chemicals such as benzene were most prevalent when moviegoers first walked into the theater. And although they diminished over the course of the film, they were present throughout.

R-rated films showed the highest levels of thirdhand smoke, even when the audience was smaller than the G-rated showings.

“During the hour-long period around R-rated movie showtime, the average emissions were equivalent to one to 10 cigarettes of secondhand smoke,” said Roger Sheu, the Yale chemical engineer who led the study, in a teleconference.

While firsthand and secondhand smoke have been known to cause health complications, there’s a possibility for complications from this newfound thirdhand smoke. Further research has to be done to examine whether factors like the type of indoor location, or even the brand of cigarettes, affect the amount of “off-gassing,” say the authors.

The Smoke That Lingers

“These results, along with past surface measurements of nicotine in nonsmoking environments, indicate that this is occurring frequently around us,” said Drew Gentner, a Yale engineer also involved in the study. “This effect is not just limited to the period [of time when the] smoker is off-gassing, but can leave a persistent contamination on the surfaces after those people leave.”

In the teleconference, Gentner and Sheu didn’t have any direct advice as to lowering the spread of thirdhand smoke. For now, Gentner says, people should be aware that the toxins are still there — even when you can’t see them.

“[Smokers] themselves remain a source of those chemicals when they go back inside,” says Gentner, “which may be particularly important in the presence of small children or sensitive populations.”