The single biggest SPF mistake isn't choosing low SPF — it's failing to reapply. Even SPF 100 sunscreen loses most of its protective power within 2 hours of going on. Picking a sunscreen comfortable enough to reapply through the day matters more than the number on the label.
Why one application isn't enough
Sunscreen degrades as it absorbs UV (that's its function). It also sweats, rubs, and oxidises off. By the 2-hour mark, you have around 50% of original protection regardless of starting SPF. By 4 hours, around 25%. UVA exposure (the deep aging wavelength) accumulates regardless of feeling sun on skin.
Formats that make reapplication realistic
Powder sunscreens over makeup
Supergoop! (Re)setting 100% Mineral Powder, Colorescience Sunforgettable. Apply with a brush; doesn't disturb base makeup. SPF 30-50.
Sunscreen sticks
Beauty of Joseon Matte Sun Stick, Tower 28 SunnyDays. Slide over face, no fuss.
Spray for body
Skim a generous layer, rub in. Reapply every 2 hours actively in sun.
Cushion compacts
Korean brands lead here (Innisfree, Missha). Quick top-up tool throughout the day.
The 'when to reapply' simple rules
Every 2 hours of outdoor exposure. After swimming or heavy sweating regardless of timing. After towelling face dry. Once a day for office-bound days (unless near a window — UVA passes through glass).
The best sunscreen is one you'll use enough of, often enough. The SPF on the label is theoretical without that.