Estimates of skin and blood concentrations of UV-filters: Insights from in vitro skin experiments

Abstract

Organic ultraviolet (UV) filters mitigate radiation transmission through the skin; however, uncertainties persist regarding their ability to cross the skin barrier and induce toxicity. Our aim was to use published in vitro skin permeation studies to predict UV-filter concentrations in blood and skin. In our review, we identified 35 papers reporting in vitro skin permeation of the 12 most used organic UV-filters. We estimated the UV-filters’ theoretical concentrations in blood and skin layers for two case scenarios and compared them with in vivo data. Five of the UV-filters penetrated skin as the parent compound, among these the highest estimated blood concentration was for benzophenone 4 (419 mg/L). These were overestimated (up to 100 times) compared to the reported in vivo results. Ten of the UV-filters permeated skin, among these ethylhexyl salicylate had the highest estimated skin concentration (15.99 g/cm³). Results from literature were inconsistent, likely due to different experimental in vitro methods. Although skin can metabolize chemicals, none of the included studies quantified potential UV-filter metabolites. We recommend future in vitro skin permeation studies to standardize the methods according to existing guidelines (including quantification of the metabolites) and screen UV-filters for possible skin absorption followed by a risk evaluation.