Drivers and passengers are breathing in potentially cancerous chemicals while in their cars, a new study finds.

The study — published May 7 in Environmental Science & Technology — analyzed the cabin air of 101 electric, gas and hybrid cars across 30 states with a model year between 2015 and 2022.

Researchers found that 99% of the cars contained a flame retardant called TCIPP, which is currently under investigation by the U.S. National Toxicology Program as a potential carcinogen. Additionally, most cars also had two more flame retardants considered carcinogenic: TDCIPP and TCEP.

The source of the cancer-causing compounds in the cabin air is seat foam, researchers said. Flame retardants have been added to seat foam to meet requirements set by the National Highway Traffic Safety Administration’s Federal Motor Vehicle Safety Standard 302, which were adopted in the 1970s and have not been updated.