Disparate SPF testing methodologies generate similar SPFs

Regulatory agencies throughout the world have developed exclusive methodologies for assessing and classifying sunscreen product efficacy in their respective markets. Three prevalent methods, the Food and Drug Administration-Final Monograph (FDA-FM) method, the Australia/New Zealand (Aus/NZ) method, and the COLIPA International (International) method, contain procedural and statistical dissimilarities with undefined significance. The objective of our clinical trials was to evaluate the influence of these disparities on sun protection factor (SPF) values. Our clinical trials evaluated the SPF of 59 test materials, using two or all three of the aforementioned methods in simultaneous trials, providing two or three SPF values for each formulation. A total of 135 trials were conducted. The consequent mean SPF values generated per trial were used to compare methods in a correlation and variance analysis. The correlation coefficients for each method pair, International vs. FDA-FM, Aus/NZ vs. FDA-FM, and International vs. Aus/NZ, were each ≥0.94. The difference in least square mean SPF for each method pair was 0.12, 0.62, and 0.81, respectively. Our juxtaposition of the mean SPFs produced by these methods clearly illustrate that any disparities between average SPF values produced by these methods are not clinically or statistically significant and that using one method should be sufficient for SPF labeling in all three respective markets.