In vivo Change of Keratin-Bound Molecules in the Human Stratum Corneum following Exposure to Ultraviolet Radiation

Background/Objectives: Ultraviolet (UV) radiation damages the stratum corneum (SC) and disrupts the skin barrier. The damaged skin changes in the molecular composition of the SC, including its water content. However, it is difficult to examine the in vivo SC changes with existing methods, so those have not been well characterized. Therefore, we investigated in vivo changes of UV-induced SC damage using confocal Raman spectroscopy. Method: We irradiated the volar forearm of 10 subjects with 0.5, 1, and 1.5 minimal erythemal doses of UV radiation. Then, we examined erythema, the transepidermal water loss (TEWL), the water content, the natural moisturizing factor (NMF), and the lipids of the skin. Results: After UV irradiation, erythema and TEWL of the skin were both increased. The bound water content of the SC was also increased following UV irradiation. The NMF of the SC revealed different tendencies. All free amino acids (FAAs) of the NMF were increased after UV irradiation, except proline. trans-urocanic acid, pyrrolidone carboxylic acid, lactate, and urea, which are NMF components produced by the subsequent catabolism of FAAs and sweat, were decreased after UV irradiation. The amount of ceramide in the SC was also decreased after UV exposure, while cholesterol was increased. Conclusions: The bound water content of the SC was increased by UV exposure along with increasing TEWL, several NMF components, and cholesterol. These in vivo results for UV-damaged SC obtained via Raman spectroscopy could be applied to research with regard to protecting the SC from UV radiation and treating UV-damaged SC.