Barrier characteristics of different human skin types investigated with X-ray diffraction, lipid analysis, and electron microscopy imaging

The stratum corneum requires ceramides, cholesterol, and fatty acids to pro vide the cutaneous permeability barrier. The lipids are organized in interc ellular membranes exhibiting short- and long-periodicity lamellar phases. I n recent years, the phase behavior of barrier lipid mixtures has been studi ed in vitro. The relationship of human stratum corneum lipid composition to membrane organization in vivo, however, has not been clearly established. Furthermore, the special function of the different ceramide species in the stratum corneum is largely unknown. We examined lipid organization and comp osition of stratum corneum sheets from different subtypes of healthy human skin (normal, dry, and aged skin). Lipid organization was investigated usin g X-ray diffraction and demonstrated that the 4.4 nm peak attributed to the long periodicity phase was frequently missing for skin with a low Cer(EOS) /Cer(total) ratio, indicating an important part for Cer(EOS), which contain s omega-hydroxy fatty acid (O) ester-linked to linoleic acid (E) and amide- linked to sphingosine (S). A deficiency in the 4.4 nm peak was predominantl y observed in young dry skin. In one case of aged skin, however, and less o ften in young normal skin this peak was also missing. Furthermore, the cera mide composition of samples without the 4.4 nm peak showed a deficiency of Cer(EOH), which contains 6-hydroxy-4-sphingenine (H), and an increase in Ce r(NS) and Cer(AS), which contain nonhydroxy (N) or alpha-hydroxy fatty acid s (A). In addition, a 3.4 nm peak attributed to crystalline cholesterol occ urred in most cases of aged and dry skin, but was not observed in young nor mal skin. Our results do not indicate a definite pattern of correlation bet ween lipid organization and types of human skin. They demonstrate, however, that Cer(EOS) and Cer(EOH) are key elements for the molecular organization of the long periodicity lamellar phase in the human stratum corneum.