Journal of the American Academy of Dermatology vol:21 issue:1 pages:56-62
Because the protection factor of sunscreens concerns only UVB protection, usually nothing is known about the protection offered in the UVA range. Using different methods, we compared six commercially available sunscreens to determine the UVA protection factor and, thus, to select the most appropriate sunscreen. Two clinical methods on human skin (inhibition of UVA-induced tanning with the use of a high-intensity UVA source and inhibition of methoxsalen plus UVA-induced phototoxicity) were compared with a method in animals (inhibition of UVA-induced sunburn cell production in mice treated with methoxsalen) and with two in vitro techniques (solution-dilution and sandwich spectrophotometry). We conclude that all five methods used give a quantitative estimate of UVA protection, but none can be accepted as a standard because the UVA protection factor varies according to the method used and the reading time.