Photoprotection by sunscreens.

Ultraviolet (UV) radiation is an etiologic factor for the development of nonmelanoma skin cancers and also possibly melanoma. The American Academy of Dermatology currently recommends the daily use of sunscreens with a sun protection factor (SPF) of 15 or above. The SPF numerical rating is an in vivo, standardized measure of sunscreen efficacy. SPF assessment predominantly reflects the ability of a product to screen UVB radiation. The physical and biologic properties of UVA radiation are relevant as UVA contributes to photoimmunosuppression and photocarcinogenesis. An ideal sunscreen assessment system would address both UVB and UVA protection. However, the SPF rating should continue to serve as the major determinant of sunscreen efficacy.