Here’s the thing most people never figure out: there are two types of ultraviolet rays coming off the sun. UVB rays are the ones that burn you — the red, painful kind you feel after a day at the beach. UVA rays are quieter. They don’t burn. They just go deep into your skin and do damage you won’t see for years.
Most glass blocks UVB almost completely. So when you’re sitting in a car or near a window, you’re right that you likely won’t burn. But according to University of Utah Health, regular glass doesn’t stop UVA — and that’s exactly the kind that keeps coming through.
UVA is what causes premature aging. Wrinkles, sun spots, leathery skin — that’s mostly UVA work, happening quietly every time you’re sitting in sunlight through a window. It also raises your risk of skin cancer, and the frustrating part is there’s no warning sign. No burn, no redness, nothing to tell you it’s happening.
This shows up in weird ways in real life. Long road trips, commuting by car every day, sitting next to a sunny window at school or work for hours — all of that adds up. UVA can pass through the kind of glass used in car side windows, house windows, and office windows, and the exposure is cumulative. Every hour counts, even when you feel nothing.
One thing worth knowing: car windshields are typically made with a laminated glass that blocks more UV than regular windows. Side and rear windows usually don’t have that same protection. So the driver’s left arm getting more sun exposure than the right arm is actually a documented thing — and over years, it can show up as noticeably more skin damage on that side.
The fix isn’t complicated. Sunscreen on exposed skin, even on low-key days. If you’re doing a long drive or sitting by a window for extended stretches, it genuinely matters. SPF 30 or higher, and make sure it says broad-spectrum on the label — that means it covers UVA, not just UVB.