Abstract
Determination of the Minimal Erythema Dose (MEDu ) 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 MEDu values for SPF testing. Individual Typology Angle and unprotected MEDu data on 9931 individuals were received from 12 laboratories located on 5 continents to determine MEDu values in prospective sunscreen testing studies. 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 MEDu and may be used to accurately predict the MEDu of an unknown test subject. 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 MEDu for the testing procedure. Use of this common ITA°-MEDu relationship will help to minimize SPF variability between testing laboratories due to use of widely varying MEDu values.
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