Quantifying the visual appearance of sunscreens applied to the skin using indirect computer image colorimetry.

BackgroundThere is no accepted method to objectively assess the visual appearance of sunscreens on the skin. MethodsWe present a method for sunscreen application, digital photography, and computer analysis to quantify the appearance of the skin after sunscreen application. Four sunscreen lotions were applied randomly at densities of 0.5, 1.0, 1.5, and 2.0mg/cm(2) to areas of the back of 29 subjects. Each application site had a matched contralateral control area. High-resolution standardized photographs including a color card were taken after sunscreen application. After color balance correction, CIE L*a*b* color values were extracted from paired sites. Differences in skin appearance attributed to sunscreen were represented by E, which in turn was calculated from the linear Euclidean distance within the L*a*b* color space between the paired sites. ResultsSunscreen visibility as measured by median E varied across different products and application densities and ranged between 1.2 and 12.1. The visibility of sunscreens varied according to product SPF, composition (organic vs inorganic), presence of tint, and baseline b* of skin (P<.05 for all). ConclusionStandardized sunscreen application followed by digital photography and indirect computer-based colorimetry represents a potential method to objectively quantify visibility of sunscreen on the skin.