Human skin in vivo has a higher skin barrier function than porcine skin ex vivo—comprehensive Raman microscopic study of the stratum corneum

Porcine skin is widely used as a human skin model in dermatology. For both, porcine stratum corneum (SC) ex vivo and human SC in vivo, the hydrogen bonding states of water, the secondary and tertiary structures of keratin, the natural moisturizing factor (NMF) concentrations and the intercellular lipids' (ICL) lateral organization are investigated depth‐dependently using confocal Raman microscopy. The SC depth profiles show that porcine SC ex vivo is characterized by lower hydrogen bonding states of water (10%‐30% SC depth), lower NMF concentration in the whole SC, more β‐sheet form of keratin (10%‐90% SC depth), more folded tertiary keratin structures (30%‐70% SC depth) and higher hexagonal lateral packing order of ICL (10%‐50% SC depth) compared to human SC in vivo. The results clearly show a higher value of skin barrier function of human SC in vivo than of porcine SC ex vivo. Thus, the human SC in vivo is less permeable for lipophilic and hydrophilic substances than porcine SC ex vivo. Considering the porcine SC as an ex vivo model of human SC in vivo, these findings should be taken into consideration. The skin barrier function‐related parameters of the stratum corneum (SC), such as intercellular lipids ordering, hydrogen bonding states of water, secondary and tertiary keratin structures, and natural moisturizing factor, have been comprehensively analyzed for all SC depths in human and porcine skin. The results clearly show a higher skin barrier function of human SC in vivo than of porcine SC ex vivo, which should be considered by using porcine skin ex vivo as an in vivo model of human skin in penetration studies.