Non-Invasive Depth Profiling of Base Cosmetic Formulations in the Skin Using Handheld Confocal Raman Spectroscopy

Ceramide-based and aqueous-based moisturizers have distinct absorption and retention characteristics in skin. Conventional methods like Transepidermal Water Loss (TEWL) and Corneometry are limited by environmental factors, and no current in vivo method measures ceramide content in skin. This research explores the use of a handheld Confocal Raman Spectroscopy (CRS) system to non-invasively analyze the absorption kinetics of these moisturizers. Measurements were taken on 40 subjects, including healthy individuals (n = 20) and those with atopic dermatitis (n = 20). Results showed that ceramide-based creams retained ceramide in the stratum corneum for longer periods, particularly 24 h post-application, compared to aqueous-based creams. Validation against Liquid Chromatography-Mass Spectrometry (LCMS) for ceramide NP in four healthy subjects showed a strong correlation (r = 0.96). These findings suggest that handheld CRS can improve the evaluation of skincare formulations, advancing the development of personalized skincare solutions.