California’s notorious traffic might be giving its commuters more than a daily dose of frustration, new research out of the University of California Riverside finds. Commuters who spend long periods of time on the highways are possibly being exposed to cancer-causing chemicals which can infiltrate dust and air inside their vehicles.

Researchers measured the levels of benzene and formaldehyde inhaled by commuters in Los Angeles, Alameda, San Diego, Orange and Santa Clara counties before the COVID-19 restrictions were put in place, basing their calculations on a mean commute time of thirty minutes. They calculated that 78 percent of these counties’ residents had at least a 10 percent chance of exceeding levels of exposure known to elevate cancer risk during their commute.

If you commute by a car for more than 20 minutes at a time, there’s a simple step you can take to help reduce your exposure to unsafe chemicals in your vehicle.

Surprisingly, these exposures came not from fuel emissions, smog or air pollution, but from two materials commonly used in the car manufacturing process. Benzene and formaldehyde, both known carcinogens, were found to exist at concentrations exceeding safe reference levels in the air inside commuter vehicles in commutes lasting twenty minutes or more.

Benzene is a common ingredient in synthetic fibers, while formaldehyde is often used as a binder when making plastics. Despite their utility, both compounds are known to be cancer-causing at high enough levels. Benzene carries the added risk of additional reproductive harm including birth defects for babies exposed in utero.

Both chemicals are known for their high volatility, meaning they are easily transferred from fabrics and plastics into the air inside the car.

Researchers emphasize that the duration and severity of the exposure matters significantly when considering how much risk is posed by carcinogen exposure during a typical commute. “There is a range of exposure that depends on how long you’re in the car, and how much of the compounds your car is emitting,” says lead study author, Aalekhya Reddam.

These findings are in line with a previous study on which Reddam and David Volz, Professor of environmental toxicology at UC Riverside collaborated. It found that longer commute times meant higher levels of exposure to another known carcinogenic compound commonly found in car seats and household dust, TDCIPP.

Safer materials in the vehicle manufacturing process would potentially eliminate the risk by avoiding the use of known carcinogens altogether, Volz points out. “There should be alternatives to these chemicals to achieve the same results in vehicle making. If so, they should be used.”

The average American commutes 26.9 minutes each way to and from work, slightly less than a typical Californian commute but still easily long enough for benzene and formaldehyde exposure to take place.

It doesn’t matter where you live. If you commute by a car for more than 20 minutes at a time, the study’s authors recommend a simple measure you can take to help reduce your exposure to unsafe chemicals in your car’s interior environment: open a window. “At least with some air flow, you’d be diluting the concentration of these chemicals in your car,” said Reddam.

The study can be found in the journal Environment International.