Chemistry & ProductsQuestion 311 of 484
A broad-spectrum SPF 30 sunscreen blocks approximately what percentage of UVB radiation when applied correctly?
a.About 97%
b.About 90%
c.Less than 50%
d.About 75%
Explanation
SPF math: SPF 15 blocks about 93% of UVB, SPF 30 about 97%, and SPF 50 about 98%. The jump from 30 to 50 only adds 1 percent more protection, so reapplication every two hours matters more than chasing a higher number.
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