BAND ANALYSIS OF HYDRATED HUMAN SKIN STRATUM CORNEUM ATTENUATED TOTAL REFLECTANCE FOURIER TRANSFORM INFRARED SPECTRA IN VIVO

Water content is an important factor for skin condition. The determination of the hydration state of the skin is necessary to obtain basic knowledge about the penetration and loss of water in the skin stratum corneum. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy is used to measure hydration of the stratum corneum. In this study we apply direct band fitting of the water bending, combination, and OH stretch bands over the 4000-650 cm(-1) wave number range. Measurements are performed on the volar aspect of the forearm using a Nicolet 800 FTIR spectrometer equipped with an ATR unit with a ZnSe crystal. Hydration of the skin is obtained by occlusion keeping the forearm pressed onto the crystal. Spectra are recorded before and after occlusion up to 30 min. The spectra are fitted with a nonlinear least-squares algorithm with Gaussian bands. Separate band fits of water, normal stratum corneum, and occluded hydrated stratum corneum spectra are obtained yielding band parameters of the individual water contributions in the bending mode at 1640 cm(-1), the combination band at 2125 cm(-1), and the OH stretches in the hydrated skin stratum corneum spectra. A scaling factor representing the contribution of the water spectrum into the skin stratum corneum spectrum is determined during the occlusion process. In comparison to the dependence of the infrared absorbance ratio in time used by Potts, our scaling factor shows a more distinct transition from enhanced signal due to increased contact area to extra signal due to water content at maximum contact area. Band fit analysis of hydrated skin stratum corneum ATR-FTIR spectra offers the possibility for quantitative determination of individual water band parameters. (C) 1998 Society of Photo-Optical Instrumentation Engineers.