How to plan sunscreen reapplication
Match the interval to what you are doing.
1
Choose the SPF
SPF 30 or higher is a common everyday choice for exposed skin.
2
Describe the activity
Swimming and heavy sweating shorten the interval regardless of SPF.
3
Set a reminder
Reapply at the interval shown, and sooner after towelling or entering the water.
What does this tool do?
SPF describes how much UVB reaches the skin, not how long a product lasts. Reapplication depends on activity, water exposure and sweating, so this tool turns those factors into a simple interval.
The Formula
Outdoors: 120 minutes; heavy sweating: 60 minutes; swimming: limited by water resistance (40 or 80 minutes)Frequently Asked Questions
Does SPF 50 last twice as long as SPF 25?
No. SPF describes how much UVB reaches the skin, not a duration. All sunscreens need reapplying after two hours in the sun and after water or heavy sweat.
How much sunscreen should I use?
About 30 ml for the body and half a teaspoon for the face and neck. Most people apply far less than the amount used in SPF testing.