How often should I reapply sunscreen if I'm sitting near a bright window?

Reapply every two hours if you’re within arm’s reach of a window getting direct sunlight — windows block UVB but let through UVA, which ages skin and raises cancer risk. If the window has UV-blocking film or you’re more than a few feet away, stretch to every 3–4 hours. On cloudy days or with tinted glass, one application in the morning is fine. Better to oversunscreen than realize too late.