I truly don’t understand how this works. I get that SPF 50 is 5 times as long as SPF 10, but WHY does it do that? Why do I need SPF 50 every 2 hours and then I start turning red?
Same question with SPF that’s a year old, does that still work like when it was bought, or not? Does the “clock” start ticking once it’s squeezed out of a tube?
In: 1
It doesn’t “know” or care how long it’s been on the skin for but the ingredients get absorbed into the skin and either broken down or transported somewhere else. That’s why it stops protecting you; the important ingredient just isn’t there anymore.
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