2026 Volume 26 Issue 9 Pages 349-356
The effects of glycerol and urea on the microstructure and water homeostasis of the stratum corneum (SC) are summarized and compared based on studies using high-brilliance synchrotron X-ray diffraction (XRD). Time-resolved XRD analyses of human SC during wetting and drying processes revealed that both glycerol and urea suppress the reduction of the coiled-coil α-helix chain distance of soft keratin during drying, indicating enhanced retention of bound water, with glycerol exhibiting a stronger effect than urea. In addition, analysis of the short lamellar structure of intercellular lipids showed that treatment with glycerol or urea prolonged the interval during which the structural volume remained unchanged, reflecting stabilization of interlamellar water within the lipid matrix. These findings indicate that glycerol and urea enhance SC water homeostasis through two complementary mechanisms: stabilization of bound water near the skin surface at approximately 25 wt% and reinforcement of water regulation by the lipid lamellar structure. Owing to these mechanisms, the water content at the SC surface is maintained homeostatically, and this homeostatic state is more effectively strengthened by glycerol than by urea.
