Optical clearing agent reduces scattering of light by the stratum corneum and modulates the physical properties of coenocytes via hydration.

ABSTRACT

BACKGROUND: The interaction between light and the skin determine how the skin looks to the human eye. Light can be absorbed, scattered, and reflected by different components of the skin in a variety of different ways. Here, we focus on the scattering properties of the outmost layer, the stratum corneum (SC). However, we currently have limited methods with which to distinguish the scattering of light by SC from the changes due to other components of the skin. MATERIALS AND METHODS: Dark-field images of tape-striped corneocytes were used in vitro to study the differences in light scattered by the SC and other skin components. Several optical clearing agents (OCAs) were tested for their ability to reduce light scattering. Physical properties of the SC (water content, keratin configuration, and volume) after OCA treatment were investigated using FT-IR, confocal Raman microscopy, and 3D laser microscopy. RESULTS: Urea derivatives, several reducing sugars, and sugar alcohols, which were used as OCA in optics and also used as humectants in cosmetic area, could reduce scattering. However, unlike dehydration in optics, penetration of water into the keratin was increased at low OCA concentrations. In such conditions, the volume of corneocytes was increased but their stiffness was reduced. CONCLUSION: By analyzing the tape-striped SC, we were able to measure the changes in the optical and physical properties of corneocytes in response to OCAs. Hydration of the SC layer by OCAs reduces light scattering from the corneocytes and would be helpful in moisturizing the skin and helping the skin look healthy.