Sunscreen standards tested with differently filtered solar simulators

Background. The COLIPA standard for solar simulators permits a range of spe ctral filtration. Published studies comparing the SPFs of sunscreen formula s show that a range of SPFs is generally expected between laboratories. Spe cifically, three studies determining the SPFs of sunscreen standards have b een performed in a series of laboratories and differences exceeding 50% hav e been reported. No studies to date have specifically examined potential di fferences in performance of Standard Sunscreen Test Formulas with varying s olar simulator spectra within the permitted range of optical filtration. Methods: In a paired clinical trial, two SPF standard sunscreen formulas we re tested using two solar simulators that complied with the COLIPA standard for solar simulators but were filtered differently. One solar simulator wa s filtered as supplied by the manufacturer and delivered a high percentage of UVB; the other solar simulator was modified by removing the visible abso rbing 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 sunscr een was almost 50% greater with the unmodified solar simulator than with th e 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, recipro city failure of the control MEDs was observed. The total intensity of the m odified lamp was approximately 3 times that of the unmodified lamp.