Sunscreen standards tested with differently filtered solar simulators.

Background: The COLIPA standard for solar simulators permits a range of spectral filtration. Published studies comparing the SPFs of sunscreen formulas show that a range of SPFs is generally expected between laboratories. Specifically, three studies determining the SPFs of sunscreen standards have been performed in a series of laboratories and differences exceeding 50% have been reported. No studies to date have specifically examined potential differences in performance of Standard Sunscreen Test Formulas with varying solar simulator spectra within the permitted range of optical filtration. Methods: In a paired clinical trial, two SPF standard sunscreen formulas were tested using two solar simulators that complied with the COLIPA standard for solar simulators but were filtered differently. One solar simulator was filtered as supplied by the manufacturer and delivered a high percentage of UVB; the other solar simulator was modified by removing the visible absorbing filter to deliver energy more closely resembling sunlight in the UVA-1 part of the spectrum, with a lower percentage of UVB. Results and Conclusion: The result was that the SPF of each standard sunscreen was almost 50% greater with the unmodified solar simulator than with the modified solar simulator. In vitro evaluation of the sunscreen standards predicted similar differences due to the spectral differences of the solar simulators, which appears to rule out reciprocity failure. However, reciprocity failure of the control MEDs was observed. The total intensity of the modified lamp was approximately 3 times that of the unmodified lamp.