Natural moisturizing factor (NMF) includes several compounds in the stratum corneum (SC), among them, urocanic acid (UCA). Ultraviolet (UV) exposure turns the trans-UCA of the SC into its cis isomer. We investigated the impact of a topical emollient emulsion treatment on the UCA isomers of the SC exposed to artificial UV stress. Aliquots of emollient emulsion were applied in healthy subjects for 2 h on delimited areas of the volar forearm, then, the SC was removed by tape stripping. Tapes were irradiated in a solar simulator chamber and a high performance liquid chromatograph was used to quantify UCA isomers from stripped SC extract. The amount of both UCA isomers were almost twice higher in the SC treated with the emollient emulsion. We also observed that the UV irradiation elevated the amount of the cis/trans UCA ratio on the SC (non-treated and treated), suggesting that the emollient sample was not able to avoid the UCA isomerization. The in vivo tests corroborated with the UCA data obtained ex vivo, since we found an increase in the superficial skin hydration with respective reduction of the TEWL, probably occurring by the occlusion performed by the emollient emulsion containing 15.0% w/w of caprylic/capric triglyceride.

Sunscreens are currently considered cosmetic assets and their use has considerably increased since consumers have become greatly aware of the damages induced by ultraviolet (UV) radiation on the skin, such as premature aging and cancer. However, concerns have arisen over the percutaneous absorption of UV filters. In order to ensure both efficacy and safety, sunscreens need to remain in the outermost layers of the stratum corneum, because their penetration into the dermis can cause systemic effects. Herein, a review was conducted of specialized literature published between 2000 to 2020, clustering studies focused on the skin penetration of UV filters. In this context, different in vitro and in vivo methodologies employed to assess the penetration of such compounds are highlighted, such as those based on tape stripping and diffusion cells. When combined with analytical methods, such as high-performance liquid chromatography, it is possible to trace a profile of the penetration of UV filters and elucidate factors that interfere with this phenomenon. Moreover, studies have been carried out on dissemination strategies that aim to encapsulate the molecules of UV filters, and/or change their physicochemical characteristics, in effort to increase the efficacy and safety of these formulations. Keywords: Franz cell; sunscreens; percutaneous penetration; tape stripping