People vigilant about shielding their skin from harmful UV rays usually reach for sunscreen when heading outdoors. Visiting several dealerships in Los Angeles, the paper’s author used a handheld UV-A light meter to gauge how much UV-A light was being passed through automotive glass. Sunscreen and DrivingClearly, car windows permit UV-A rays to penetrate into the cabin. The Skin Cancer Foundation echoes this advice, adding that babies secured in the back passenger seats should also be protected. Car windows don’t do a great job of blocking UV rays, but sunscreen does.