Body & HealthFact

SPF 50 doesn't protect twice as well as SPF 25.

Sun protection factor states what fraction of UV-B gets through: SPF 15 lets through 1/15 (about 7 %), SPF 30 about 3 %, SPF 50 about 2 %. So the jump from 30 to 50 gains only one percentage point. More important than the number is the amount: most people apply just a quarter to a half of the tested 2 mg per cm².

Useful: A full-body application for an adult takes about 30–40 ml – a shot glass.

Source: en.wikipedia.org

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