Sun protection factor testing: comparison of fda and din methods

Abstract

The sun protection factor (SPF) is a dimensionless ratio that estimates the protective efficacy of a sunscreen against acute damage. SPF values of several sunscreens were measured by three protocols: (1) the FDA sequential technique, in which successive sites are exposed to a constant source for progressively longer time periods, varying by 25% intervals; (2) the DIN simultaneous technique, in which all sites are exposed simultaneously to a constant source and sequentially occluded to provide exposure steps varying by 40%; (3) a series-sequential technique in which six sites are exposed simultaneously to a multiport source with selectable intensity gradations of 25%. Methods 1 and 3 utilize xenon arc solar simulators, whereas method 2 uses the Osram Ultravitalux mercury vapor lamp source. The FDA and DIN testing procedures differ in their radiation source, application amounts, exposure regimens, and data evaluation, and may produce similar or different results with different sunscreens. Reasons for observed discrepancies are discussed. Fluence estimates represented by measured time at constant intensity or by measured intensity for constant time are equally satisfactory for SPF evaluation.