[Research] Reapplication of sunscreen

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The notion that you have to reapply sunscreen every few hours persists since quite a long time. In the past few years some research was done on this topic. Two papers done with human subjects and the conclusions:1 - 8 hours after application, sunscreen still retained ~75% of its SPF in people who were just hanging out2 - 8 hours after application, sunscreen retained ~43% of its SPF in people who performed physical activity in a hot environment and bathedAn SPF 50 sunscreen after 8 hours under extreme conditions should still provide a decent SPF of 21. Under normal conditions reapplication likely is unnecessary as long as the sunscreen is photostable and possibly water resistant. The SPF barely declined past the first 4 hours.There was no difference between organic / inorganic sunscreens, as some people used to think only mineral sunscreens are an exception to the reapplication rule. For the average person using an SPF 50 sunscreen in the morning, you'll still have ~ SPF 35+ when you go home in the evening. There is nothing wrong with reapplication, but you likely don't have to feel guilty if you don't.
Girls Blog 2015
Submitted by DieMafia