Flame Retardants in Cars May Increase Exposure to Carcinogens

Flame retardants used in car interior surfaces can pollute the cabin air with chemicals associated with cancer, according to a study published May 7 in Environmental Science & Technology.

Researchers discovered the presence of carcinogenic and possibly carcinogenic flame retardants in the seat foam of virtually all of the cars they tested—101 personal vehicles manufactured between 2015 and 2022. What’s more, they also found those same chemicals in the air inside the car.

Manufacturers have added flame retardants to cars since 1971, when the National Highway Traffic Safety Administration required their use to slow the spread of potential fires. But some experts say they aren’t always effective, and the new study indicates a major unintended side effect: the regular inhalation of hazardous chemicals by countless drivers and passengers.

“Outdated safety standards that are supposed to protect our safety are leading to harmful chemical exposure,” Lydia Jahl, PhD, a senior scientist at the Green Science Policy Institute in Berkeley, California, who co-authored the study, told Health.

The authors said the new research was inspired by a 2020 study that found that college students who had longer commutes to school were exposed to higher amounts of tris(1,3-dichloro-2-propyl) phosphate (TDCIPP), which California’s Proposition 65 lists as a carcinogen.

For the new study, Jahl and her team tested seat foam and cabin air in the vehicles of the more than 100 electric, gas, and hybrid cars across 30 states. They discovered that, in both the foam and air, 99% of the vehicles contained a chemical flame retardant called tris(1-chloro-isopropyl) phosphate (TCIPP), which is under investigation by the U.S. National Toxicology Program as a potential carcinogen.

Researchers have also linked TCIPP with reproductive issues in rodent studies, as well as gastrointestinal cancers in some studies involving humans. 

Most cars had more than one flame retardant. In addition to finding TDCIPP, researchers discovered another chemical designated by California as a carcinogen: tris(2-chloroethyl) phosphate (TCEP). Both substances have also been linked to neurological and reproductive health concerns, researchers said.

Overall, the concentration of air particles from fire retardants was two to five times higher in the summer than in the winter. Levels of TCIPP averaged four times higher than other chemicals during the winter months and nine times higher in the summer.

Michael Levine, MD, an associate professor of emergency medicine and emergency medicine physician and medical toxicologist at the University of California, Los Angeles, told Health that there is simply not enough information to know how inhaling these chemicals while in the car may affect health.

“Just because something is carcinogenic, it doesn’t mean it will cause cancer, nor is it necessarily carcinogenic at these levels people are exposed to in their cars,” he said. “You have to factor in the overall lifetime exposure before you determine if something is dangerous, and we don’t have this from this study.”

He added that some of the flame retardants found are only under investigation for being carcinogenic, which means they haven’t yet been proven to cause harm.

Jahl said there are some steps you can take to reduce potential exposure to carcinogenic particles while in the car.

She suggests rolling down the windows when you first get in the car, especially in summer, and keeping them down for at least a few minutes. During longer road trips, open the windows for a bit every couple of hours to flush the cabin with fresh air.

And, unless you’re driving in an area with heavy traffic (and therefore lots of exhaust pollution), avoid circulating cabin air.

In response to the study, Consumer Reports launched a petition to reverse the 1971 NHTSA regulation that requires this, calling the rule “outdated.”

Sean DeCrane, director firefighter health and safety operational services for the International Association of Fire Fighters in Washington D.C., argued the risk of carcinogen exposure outweighs the benefits of flame retardants in the event of a fire.

Flame retardants are “not slowing down the fire at a rate that is worth the long-term exposure to the fire retardants,” he told Health. Plus, when the foam starts to burn, many flame retardants can actually worsen air quality by releasing chemicals, he added.

The researchers are also calling on NHTSA to update their flammability standard for vehicles, Jahl said. “Most people are in a vehicle, even if they don’t own one, at least once a week. And people who are cab or rideshare drivers or people who make the cars have an even higher exposure.”