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When should you reapply sunscreen?
☀ 3 min read · Sun & tanning guide
The rule of thumb is every two hours - and immediately after swimming, heavy sweating or towelling off. Sunscreen wears down, rubs off and breaks down in UV.
Even a perfect first application doesn't last all day. Sunscreen degrades as it absorbs UV, and it physically comes off through sweat, water, sand and contact with clothing. That's why the “apply once in the morning” approach leaves most people under-protected by lunchtime.
The reapplication rules
- Every 2 hours during ongoing sun exposure.
- Right after swimming - even “water resistant” SPF is only rated for 40–80 minutes in water.
- After heavy sweating or wiping your skin with a towel.
- Higher UV, shorter intervals. On a very-high-UV day, don't stretch past two hours.
Application beats reapplication mistakes
Two common errors undo everything: using too little (aim for about a shot-glass amount for the body) and missing spots - ears, back of the neck, tops of feet, hairline. Reapplication is your chance to fix both. Note that reapplying doesn't “reset the clock” on total UV dose - it maintains the protection you started with. For why SPF still lets you tan, see does SPF stop tanning?
The hard part: remembering
The two-hour rule is simple; remembering it mid-beach-day is not. A phone in a bag doesn't help - which is exactly the gap a timer fills.
Do it in Sunhalo
Sunhalo turns the two-hour rule into active session coaching. Start a session and it runs a protection timer with reapplication prompts and shade breaks, adjusted for the live UV and your SPF. The countdown lives on your Lock Screen as a Live Activity, so it keeps reminding you even while your phone is tucked away - no mental math required.
Frequently asked
Do you need to reapply sunscreen if you stay dry?
Yes. Sunscreen still degrades in UV and rubs off on clothing, so reapply every two hours even without swimming or sweating.
Is water-resistant sunscreen enough for swimming?
No. Water-resistant SPF is only rated for 40-80 minutes in water, so reapply as soon as you towel off.
Does reapplying let me stay out longer safely?
Not indefinitely. Reapplying maintains protection but doesn't erase accumulated UV dose - take shade breaks and watch the UV index too.
Keep reading
Sunhalo provides educational estimates, not medical advice, and is not a medical device. Any tan is a sign of UV damage. Medications, altitude, and reflection off water, sand or snow all change your real risk. When in doubt, choose shade.
