Global data of unprotected skin minimal erythema dose relationship to Individual Typology Angle

Background Determination of the Minimal Erythema Dose (MED u ) of unprotected skin is perhaps the most critical aspect of the Sun Protection Factor (SPF) value and disproportionately influences the SPF. Individual Typology Angle (ITA°), a skin reflectance measure of the skin's pigmentation, has been used by many clinical laboratories to estimate the MED u values for SPF testing. Methods Individual Typology Angle and unprotected MED u data on 9931 individuals were received from 12 laboratories located on 5 continents to determine MED u values in prospective sunscreen testing studies. Results These data were compiled and normalized by laboratory (to account for differences in number of subjects within each laboratory). A polynomial regression best fits the relationship between ITA° and their MED u and may be used to accurately predict the MED u of an unknown test subject. Conclusion The regression data have been incorporated into the latest ISO24444 (Cosmetics – Protection test methods – in vivo determination of the sun protection factor (SPF), 2019) in vivo Sunscreen testing method that must be utilized to determine a subject's provisional MED u for the testing procedure. Use of this common ITA°‐MED u relationship will help to minimize SPF variability between testing laboratories due to use of widely varying MED u values.