Characterization of skin moisture and evaluation of cosmetic moisturizing properties using miniature near-infrared spectrometer

The miniature near-infrared (NIR) spectrometer has been modified to be more appropriate for the acquisition of NIR spectra on the skin surface and for non-contact detection. Principal component analysis (PCA) was applied to the monitoring of moisture loss from isolated porcine skin and showed a strong linear relationship between the first principal component score of the NIR spectra and the moisture content, with a high correlation coefficient of 0.98. Afterward, by continuously monitoring NIR spectra on the skin of volunteers treated with five different traits of moisturizing products and using PCA to investigate the spectra obtained over time, we examined the feasibility of NIR spectroscopy for skin surface moisture detection, thus assessed the in vivo moisturizing and water retention capacity of different moisturizer products. This work provides a reference for the direct application of the miniature NIR spectrometer to the detection of in vivo moisturizing efficiency of cosmetics and skin hydration.