Everyone knows that a long day out in the sun is harmful for your skin. But did you know driving on a sunny day can be dangerous too?

Your sun exposure doesn’t stop when you decide to head home from a beach day. A recent FOX9 news investigation interviewed Board-certified dermatologist Dr. Matthew Larson of Dermatology Consultants and 3M experts on the hidden dangers of long car trips. The story was based on a new study reporting that windshields and sunroofs do an adequate job of blocking ultraviolet rays, but side windows of a car hardly help at all.

This means that when you’re in the driver’s seat, the left side of your body is exposed to roughly 60% of the sun’s UV rays. It may not seem like you’re getting burnt, but a couple hours in a car with the sun beating down on your left forearm can become a problem after a while. People with lengthy commutes will see their total sun exposure pile up quickly, and may be at increased risk for skin cancer.

There are ways to lessen the effects of UV rays, but they’ll cost you. Tinted windows do a much better job than standard car windows, and block over 90% of UV rays. Replacing your current windows with tinted alternatives can cost hundreds of dollars. Consider wearing sunscreen in the car before a long road trip to try to mitigate some of the hidden danger that the sun poses.