In a 2015 study published in JAMA Dermatology, researchers discovered that pilots flying for 56.6 minutes at 30,000 feet receive the same amount of UVA radiation as you'd get from a 20-minute tanning bed session. Apparently, the windshield blocks UVB rays, but not UVA, which penetrates the skin more deeply than UVB and causes skin aging, wrinkling, and damages skin cells on the basal layer where most skin cancers occur. What's even more frightening is that when flying over clouds and snow (where more light is reflected), these effects could be even worse. So while you're probably not flying in the cockpit during a flight and won't have as large an amount of sunlight hitting you from all angles, according to an article in Allure, even when you're sitting in the cabin, the UV rays are much more intense at higher altitudes, and with thinner air, there is less screening of harmful radiation.
Perhaps you've seen the viral photo of the truck driver in which the left side of his face had intense photodamage, wrinkling, and thickening from directly facing the sun for 28 years. That was on the ground—imagine what frequent flyers would experience sitting closer to the sun.
So how can you avoid this from happening in the future? Contrary to what you may be thinking, booking a window seat is actually ideal. This way, you have the ability to control the shade and keep it down the entire flight. But if you're in the middle or aisle seat, first, make friends with whomever's sitting near the window, and then ask them to close it for their own skin health and yours. All kidding aside, make sure to pack a sunscreen in your carry-on to reapply throughout the flight. We recommend Bare Republic Mineral Sport Stick ($10) for mess-free application. Just don't forget about your neck, chest, ears, hands—anywhere that's exposed!