2 doctors weighed in:

How is the sun protection factor measured?

2 doctors weighed in
Dr. Michael Fisher
Dermatology
1 doctor agrees

In brief: 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.

In brief: 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.
Dr. Michael Fisher
Dr. Michael Fisher
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