Mid‐Infrared Absorption Coefficients of Human Skin Stratum Corneum

We report infrared absorption coefficients of human stratum corneum (SC) from both native ex vivo tissue and in vitro skin models. While the optical properties of human SC have been extensively characterized in the visible and near‐infrared spectral ranges, data on its mid‐infrared (Mid‐IR) absorption characteristics remain limited and largely qualitative. By using transmission infrared (IR) spectroscopy, we provide a quantitative dataset of Mid‐IR absorption coefficients. Furthermore, we investigate the dependence of the absorption coefficients on sample hydration offering insights into how water content influences Mid‐IR optical properties. The SC shows a good transparency in the so‐called molecular fingerprint region (1500 to 950 cm), even in high relative humidity conditions. Our results show that native and in vitro SC exhibit nearly identical spectra, with only minor deviations that can be attributed to chemicals used for fixation of the native skin. With our results, we provide a quantitative foundation for understanding the interaction of Mid‐IR light with skin. As the primary interface for incident light, data on the SC's absorption provides also a basis for advancing noninvasive Mid‐IR applications in biomedical sensing and dermatological research.