You need sunscreen in a plane window seat if you're flying in daylight. Standard cabin windows block most UVB but let UVA through, and at cruising altitude you're closer to a stronger sun with little more than that pane between you. UVA is the aging wavelength. It won't burn you in seat 14A, but on long flights it quietly adds up.
What the Window Does and Doesn't Block
Window glass and acrylic are good UVB filters, which is why you won't sunburn mid-flight. UVA penetrates glass far more readily, reaches deeper into skin, and drives photoaging. It's the reason pilots and frequent daytime flyers show measurable sun damage.
The Window-Seat Routine
Apply SPF before boarding like any other morning. Sun streaming in on your side? Shut the shade. It's the lowest-effort sun protection in aviation. Before landing on a long flight, top up so you walk out of the terminal already protected. Packing rules and the full travel kit live in our guide to taking sunscreen on a plane.
At Naked Sundays, we make minis and travel duos designed to clear TSA's liquids rule, because protection that can't board with you protects nobody.
Bottom Line
Aisle seat at night: skip it. Window seat in daylight, especially long-haul: SPF on, shade down when the sun swings your way.