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.

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.

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.