How Often Should You Reapply Sunscreen?

Where the two-hour rule comes from

Sunscreen does not fail all at once. It wears down through rubbing, sweat, water, and the simple breakdown of the active ingredients in sunlight. Roughly two hours is a sensible default for average conditions, which is why it is the standard advice. The problem is that few days are average.

What actually changes the interval

• →UV strength: a UV of 10 burns through protection faster than a UV of 4, so high-UV days need earlier reapplication.
• →Swimming and sweat: reapply right after toweling off, even water-resistant formulas, because they only resist water for a limited time.
• →How much you applied: most people use far too little. A thin layer protects for less time than the label assumes.

The first application matters most

Reapplication only tops up what you started with. Apply a generous layer 15 minutes before you go out so it has time to bind to your skin, cover the easy-to-miss spots like ears, neck, tops of feet, and hairline, and then keep it topped up. A great reapplication routine cannot fix a stingy first coat.

The real problem is remembering

Most sunburns do not happen because someone did not know the rule. They happen because two hours passed unnoticed on a good day at the beach. The fix is to take the remembering off your plate.

Sunly times your reapply reminder to the sunscreen you used and the live UV, so it nudges you sooner on a fierce day and later on a mild one. It also sends a high-UV alert if conditions spike. See how it works on the sunscreen reminder page, or check today's level with the UV index tracker.

A quick checklist

• →Apply generously 15 minutes before going out.
• →Reapply roughly every two hours, sooner when the UV is high.
• →Always reapply after swimming, sweating, or toweling off.
• →Let Sunly remind you so you never have to track the time.