The skin is the largest organ of the human body, accounting for ~10% of the body weight. The quality of its state and functionality is essential for the human health. Dry skin is a common phenomenon in various physiopathological dysfunctions. The uppermost layer of the skin, the stratum corneum assumes the first barrier between organism and environment, it is thus considered as the main element controlling skin hydration. This work, combining technical and methodological developments, led to highlight the molecular mechanisms involved in skin dryness phenomena by confocal Raman microspectroscopy. The molecular link between hydration and mechanical stress of SC ex vivo is described in detail involving lipids and proteins. This work has also focused on the characterization of supramolecular changes related to the deformations of the SC under mechanical stress. In parallel, this work illustrates the effectiveness of vibrational spectroscopy for evaluation of moisturizers mechanisms of action. The non-invasive nature of Raman spectroscopy allowed exploiting the high potential of this technique by transposing spectral descriptors obtained ex vivo to in vivo. Thus, we developed an in vivo approach coupling Raman spectroscopy and partial least squares method (PLS) for indirect quantification of different physico-chemical and functional parameters including the SC lipids and water leading to an overall characterization of the SC physiopathological status.
