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by treis 290 days ago
That isn't how sunscreen works. If you put SPF 50 on and spend 8 hours in the sun you're coming back a lobster.

Say you burn in 5 minutes. SPF 50 means you burn in 250 minutes. But it's more like 100% protection for 245 minutes and then 0% for the last 5. It's not a steady cooking at 2.5% intensity.
1 comments
rcxdude 289 days ago
Got any source for that? Everything I can find (and the intuitive explanation of it) points to the opposite: SPF is how much of the UV blocks, not at all how long the sunscreen stays on your skin (which varies wildly with what you're doing).
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treis 289 days ago
https://cdnmedia.eurofins.com/apac/media/609921/spf-iso-prot...

That's my entire point. The way they generate SPF measures how much of the sun it blocks in the lab shortly after it's applied. That one blocks 97.5% and another 98% is meaningless for the real world.

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