Although smoking bans help protect nonsmokers from secondhand smoke, they don’t completely eliminate people’s exposure to the hazardous chemicals released by other people’s cigarettes.

There’s still the matter of thirdhand smoke — the chemical residue in tobacco smoke that clings to clothing, hair, skin, carpets, furniture, walls and other materials after the cigarette is extinguished.

And, yes, that residue attaches itself to smokers even when they smoke outside.

Concerns about the health risks associated with thirdhand smoke have been growing, particularly for infants and young children. One study calculated that the health damage from thirdhand smoke may account for up to 60 percent of the harm attributed to secondhand smoke.

Previous studies on thirdhand smoke were able to identify notable quantities of nicotine and other tobacco-related chemical compounds in rooms that had been previously smoked in.  The authors of a new study, published Wednesday in the journal Science Advances, have taken that research further. They tracked and measured traces of cigarette smoke in an environment where no smoking had occurred for many years — a German movie theater.

What they discovered is not reassuring. Their findings suggest that even when we’re in a room where no one has smoked, we can be exposed to the hazardous chemicals of cigarette smoke, depending on who is in the room with us — or who has been there previously.

“People are substantial carriers of third-hand smoke contaminants to other environments,” says Drew Gentner, the study’s senior author and an associate professor of chemical and environmental engineering at Yale University, in a released statement.  “So, the idea that someone is protected from the potential health effects of cigarette smoke because they’re not directly exposed to second-hand smoke is not the case.”

Tracing the source

For the study, Gentner and his colleagues placed a mass spectrometer — a device that can detect and measure chemicals — near one of the air ducts in a movie theater in Mainz, Germany. Smoking had been banned in the 14,000-square-foot theater for 15 years, and the air in the building was fresh (from outside), filtered and continuously ventilated.

The researchers monitored the air for four days, measuring its chemical content before, during and after the theater’s four to five daily showings of films.

They found that the air contained 35 volatile substances found in tobacco smoke, including cancer-causing chemicals like formaldehyde and benzene. They also found that the levels of these substances spiked when moviegoers entered the building.

Although the chemical levels fell during the showing of each film, they didn’t completely disappear. Some tobacco-related contamination could be detected in the theater on the mornings after the showings, when the building was empty.

“That’s because the chemicals don’t remain entirely in the air, but are also absorbed on to various surfaces and furnishings from which they re-enter the air over time,” said Gentner in an interview with Guardian reporter Nicola Davis.

The data also revealed some other interesting patterns. The chemical levels were about 200 percent higher during the theater’s later showings, which featured R-rated films, then during the earlier showings, which tended to be family films — even though the later showings had smaller audiences.

As Gentner explained to David, “In the R-rated films, especially the ones that are occurring later in the evening, it appears there’s a greater propensity of people attending those movies to have smoked, or perhaps to have smoked more frequently or more cigarettes, and so they are off-gassing more.”

During the R-rated movies, the people in the theater’s audience were exposed to the equivalent of secondhand smoke from between one and 10 cigarettes, depending on which substance was being measured, Gentner and his colleagues concluded.

Limitations and implications

This study involved a single theater in a single European city. Its findings may or may not be applicable to other environments.

Also, it’s not clear if the levels of thirdhand smoke detected in the study are high enough to lead to health problems.

Still, the findings are concerning, particularly since the German theater was a relatively large space with good ventilation.

Spaces that are smaller and more poorly ventilated, such as bars, public transit, offices and homes, are likely to have much higher levels of contaminants from thirdhand smoke, the researchers point out.

FMI: You can read the study in full on the website for Science Advances.