We all know the clouds of noxious fumes coming out of our vehicle tailpipes are a health hazard. Another part of your car, however, might produce an even more dangerous hazard to the lungs.

The brakes.

British researchers found in a recent study that the particles released by brakes might actually be more of a health threat than diesel exhaust. And while exhaust is the focus of anti-pollution efforts, brake dust is mostly unregulated.

Don’t think this is a minor annoyance. Researchers found that most particles produced by traffic in urban areas come from vehicle brakes.

The scientists found that some common, copper-rich brake pads cause more stress and damage in lung cells than diesel fumes. The copper accumulates in the cells, can trigger an inflammatory response and is thought to be the main driver of the danger.

Another risk is that the copper can lead cells to behave as if they’re starved for oxygen when they are not. This can lead to cancer and debilitating lung scarring.

Ironically, electric vehicles might exacerbate the problem. That’s because their batteries make them heavier than many gas-guzzlers. This produces more brake dust as the brakes work harder to slow the car.

So, scientists say, a manufacturer would be inaccurate when describing an electric model as being “zero-emission.”

A few states restrict the amount of copper allowed in brake pads, including California and Washington. The restrictions, however, were enacted solely to protect fish and aquatic species. The worry was that the copper would wash off roadways and into waterways.

Nonetheless, it’s now clear these laws protect fish and human alike.