Photoprotective adaptation. Some quantitative aspects.

The magnitude and time course of UV radiation-induced photoprotection was investigated in fair-skinned volunteers. Resistance to sunburn was evident three days following single exposures to UV-B, reached a maximum by seven days, and declined gradually over a period of 30 to 40 days. Both the magnitude and time course of UV radiation-induced photoprotection were dose related. The maximal mean protection factor following an exposure to 2 minimal erythemal doses was 4.2. The present findings, along with earlier studies, suggest that there are pronounced spectral differences with regard to the induction of photoprotective adaptation and that UV-B wavelengths are the most effective.