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The enzyme sphingomyelinase (sphingomyelin phosphorylcholine phosphohydrolase E.C.3.1.4.12) which hydrolyzes sphingomyelin to ceramide (N-acylsphingosine) and phosphorylcholine was identified in the subcellular fractions of pig and human epidermis. The enzyme has an optimum pH of 4.5 to 5 and is activated by Triton X-100 (0.1% w/v). Approximately two-thirds of the enzyme activity in both the pig and human epidermal homogenates was in the soluble subcellular fraction and more than half of the enzyme activity in the subcellular particulate fraction was solubilized by freeze-thawing. The pH optimum suggests that epidermal sphingomyelinase is probably a lysozomal enzyme. The enzymes in both pig and human epidermis exhibited Michaelis-Menten kinetics. The soluble sphingomyelinase in pig epidermis had an apparent Km, 4.5 X 10(-5) M and that in human epidermis an apparent Km 7.7 X 10(-5) M. The pig epidermal sphingomyelinase had no special requirement for either divalent or heavy metal ions and was not inhibited by sulfydryl group-blocking agents but it was moderately inhibited by dithiothreitol. No evidence was found in either pig or human epidermis for the presence of a phospholipase C (E.C.3.1.4.3) which hydrolyzes phosphatidylcholine to diglyceride and phosphorylcholine but there was suggestive evidence of another catabolic pathway for phosphatidylcholine.

We have isolated the lowest region of human and pig stratum corneum as an integral layer which we have termed the stratum compactum. This preparation is resistant to disruption by enzymes, 6 M urea, Triton X-100 and solvents. Our evidence suggests that all cells of the stratum corneum may be equally permeable to aqueous soluble materials but that penetration of materials through the corneum depends on the state of cohesion between cells and of the organization of intercellular lipid species. As the cells move up towards the outside of the stratum corneum the cohesive forces are reduced due to desmosome degradation and lipid modifications with ultimate dyshesion and sloughing of individual cells.

Synopsis A vast array of cosmetic products are used routinely by consumers to alleviate a range of skin care problems. Consumer concern ranges from age-associated skin changes to complexion (e.g., spots and pimples) and dryness. However, a major cause for concern amongst European female consumers is skin dryness, which spans all age ranges and skin types. Utilizing instrumental procedures (Squametry and Image Analysis) the severity of skin dryness has been correlated with expert assessment and consumer perception of dryness. The sensitivity of these techniques enables one to follow the progression of dryness alleviation for a range of product forms (e.g., creams and lotions) as well as the purported mechanism of action of various ingredient systems (e.g., occlusivity, moisturization). While conventional cosmetic products are shown to be effective, these techniques can be used to aid in the assessment and formulation of more effective products. Efficacité des produit cosmétiques à l'allégement d'un spectre d'états de peau sèche selon des measures cliniques et au moyen d'instruments.