A Comparison of Sun Protective Factor (SPF) Determinations in Guinea Pigs and Humans Utilizing Artificial Light

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Abstract
A screening method for determining sun protection factor (SPF) values of prototype sunscreen formulations has been developed using guinea pigs. Two sets of experiments were done to substantiate the guinea pig as a reliable model for SPF determinations. In the first set of experiments, SPFs of two commercially available sunscreens and a homosalate control were determined in guinea pigs and human subjects, using artificial light. Statistical analysis of data for the two commercial products confirmed that the guinea pig model could successfully predict the SPF values established by human testing. The average SPF value obtained in guinea pigs using 8% homosalate was significantly different when compared to the human test. A second set of experiments compared the claimed SPF on the packages of four commercially available sunscreens with SPF values determined in the guinea pig test. The average SPF values experimentally derived in the guinea pig were not statistically different from the claimed values. The results of these studies demonstrate that the guinea pig is a reliable model to screen for SPF values of prototype sunscreen products. This guinea pig method is not meant to be a substitute for human data, which are necessary to substantiate a claimed SPF on a commercial package. The method in the FDA Proposed Sunscreen Monograph (human testing) must still be used for that purpose.

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