Confocal Raman spectroscopy: In vivo biochemical changes in the human skin by topical formulations under UV radiation

•Polymer gels as delivery systems of MAA and Gad were prepared.•In vivo photoprotection of MAA and Gad was evaluated under UV exposure.•In vivo confocal Raman measurements showed biochemical changes in the human skin.•Relative concentrations of t-UCA and HIS were calculated from the Raman spectra.

A new approach to the study of the effects on human skin of mycosporine-like amino acids (MAAs) and gadusol (Gad) incorporated in polymer gel is proposed in this work. The depth profile and photoprotector effects of Pluronic F127® gels containing each of the natural actives were evaluated by in vivo confocal Raman spectroscopy aiming at the analysis of the biochemical changes on human skin. Hierarchical cluster analysis (HCA) showed that the data corresponding to different depths of the skin, from surface to 4 μm, and from 6 to 16 μm, remained in the same cluster. In vivo Raman spectra, classified into five different layers of epidermis according to their similarities, indicated that the amount of Gad gel increased by about 26% in the outermost layer of the stratum corneum (SC) and that MAAs gel at 2 μm depth was 103.4% higher than in the outermost layer of the SC. Variations in the SC of urocanic acid at 1490–1515 cm− 1 and 1652 cm− 1 and histidine at 1318 cm− 1 were calculated, before and after UV exposure with or without gels. With the application of gels the vibrational modes that correspond to lipids in trans conformation (1063 and 1128 cm− 1) increased with respect to normal skin, whereas gauche conformation (1085 cm− 1) disappeared. Our studies suggest that gels protected the skin against the stress of the natural defense mechanism caused by high levels of UV exposure.