The use of flame retardants in auto interior seats pollutes the air in car cabins with the highly toxic chemicals, putting those who spend significant time in cars at the most risk, peer-reviewed research in the US has found.

About 99% of car-interior air samples contained at least one flame retardant the government considers a carcinogen or potential carcinogen, and most show additional, similar flame retardants linked to reproductive disorders and neurological problems, including reduced IQ in children.

“Considering the average driver spends about an hour in the car every day, this is a significant public health issue,” said lead author Rebecca Hoehn, a Duke University researcher. “It’s particularly concerning for drivers with longer commutes as well as child passengers, who breathe more air pound for pound than adults.”

Flame retardants are added to seat foam to meet regulations the US National Highway Traffic Safety Administration implemented in the 1970s that require automakers to include flame retardants to prevent the ignition and spreading of fires.

But the chemicals’ effectiveness was overstated at the time, and their toxicity was not understood. Flame retardants do “little to prevent fires for most uses and instead makes the blazes smokier and more toxic for victims, and especially for first responders”, said Patrick Morrison, director of the International Association of Fire Fighters’ safety division.

The study checked air inside the cabins of 101 cars from model year 2015 or newer. Virtually all air samples contained 1-chloro-isopropyl phosphate, a flame retardant considered by the US National Toxicology Program to be a potential carcinogen.

Most also showed organophosphate ester flame retardants, which in children are thought to cause asthma, early growth, adiposity and brain damage. Meanwhile, two of the chemicals are listed as California Proposition 65 carcinogens, and people with the highest levels of some flame retardants in their blood have about four times the risk of dying from cancer.

The average US child has lost three to five IQ points from exposure to one flame retardant used in cars and furniture, epidemiological studies have shown.

The research also found higher levels in the summer because seats give off gas at higher rates in warmer weather. Parking in shade or rolling down windows can help, but the study’s authors say the real solution is to eliminate the use of flame retardants in cars. As the flame retardants’ ineffectiveness has become clearer, some states have reduced their use in furniture, and the federal government has taken steps to begin limiting some classes of the chemicals.