Product application technique alters the sun protection factor.

A number of factors may alter the efficacy of a sunscreen product being tested. Notably among these are (1) the source of ultraviolet (UV) radiation, (2) the filtration of the UV radiation source, (3) such environmental factors as swimming or sweating (4) and/or the amount of product applied. This is the first report in which the technique of product application itself is examined. We find that the act of rubbing the product into the skin appears also to remove product from the skin. In our study, different techniques of product application produced a 25% deviation in product sun protection factor. The variables associated with the application of sunscreening products are discussed.