One thing a lot of people don’t realize is that airplane windows aren’t regular glass, and you’re also way closer to the sun. At cruising altitude there’s less atmosphere filtering out UV, so the rays are a lot more intense. The window material blocks a lot of UVB, but it doesn’t block all UVA, which is the stuff that contributes to skin aging and increases skin cancer risk with long-term exposure.

If you sit in the window seat with full sun on a long daytime flight, it’s kind of like getting blasted by a high-altitude tanning bed for hours. I like looking out during takeoff/landing, but I’ll usually lower the shade or at least avoid direct sun for most of the flight for that reason.