How does the PA/PPD system work?

I've been reading about sunscreens, and I'm a bit confused about the PPD/PA system. Does it work the same as SPF? For example, an SPF 50 sunscreen works about as well as an SPF 100 sunscreen. Does the same thing apply to sunscreens with a PPD rating of 16 and 40?


  • This is a great question that comes up a lot. I'll talk to Perry about discussing it on a future podcast. In the meantime here's a link to a video that gives you some good background on the different systems. 

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