How often should I reapply sunscreen?

Reapply every two hours if you’re outside, even if you don’t feel sweaty, because UV exposure is cumulative and sunscreen breaks down from UV, not just sweat. If you’re indoors near windows, reapply at least midday since UVA goes through glass and causes damage over time. Set a timer if needed — your skin doesn’t care if reapplying is annoying.