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A member asked:
How is the sun protection factor measured?
A doctor has provided 1 answer
SPF: Spf stands for sun protection factor. The number is determined experimentally indoors by exposing human subjects to a light spectrum meant to mimic noontime sun. Some subjects wear sunscreen and others do not. The amount of light that induces redness in sunscreen-protected skin, divided by the amount of light that induces redness in unprotected skin is the spf. It is mainly a measure of uvb protec.
Answered 5/11/2012
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