Raman spectroscopy: feasibility of in vivo survey of stratum corneum lipids, effect of natural aging.

The main function of the stratum corneum (SC) is for protection against external aggression. This is described as the barrier function. It mainly depends on the presence of a lipid matrix composed of ceramides, free fatty acids, cholesterol and its derivatives in the intercellular spaces. Previous studies have reported the application of Raman spectroscopy to reveal the organization of SC lipids and the state of their barrier functions. Several spectral features are directly informative about the lateral packing and the conformational order. In this work, in vivo Raman spectroscopy is used to asses the state of the SC lipid content and thus its barrier function, directly on the skin. To study the effect of natural aging on the organization of these lipids, spectra were collected from the internal side of the forearms of twenty volunteers aged from 22 to 64. Multivariate data processing enabled separation of the in vivo spectra according to the volunteers' ages. Spectral signatures show small variations, indicating a slight change in the lateral packing of SC lipids with aging of the skin.