Sunscreen Effectiveness: Theoretical and Practical Considerations*

S ummary This paper examines the theoretical and practical considerations which may limit sunscreen effectiveness and lead to false expectations on the part of sunscreen users. Present evidence for a preventative effect against carcinogenesis and long term damage is inadequate and needs more attention. Determination of more meaningful protection factors requires better replication of field conditions and better definition of the best parameter, in the acute stage, which would correlate with long term damage. Careful patient instruction with regard to time, site and frequency of application is required. The importance of protection from suberythemal damage, reason for application and maximizing physical protection and avoidance, should be stressed.