Development of a stratum corneum lipid model to study the cutaneous moisture barrier properties

Abstract A skin lipid model to study barrier properties of stratum corneum has been developed. Research that led to the evolution of this model is presented along with highlights of recent findings. At normal water content of skin, the model lipid exists as a liquid crystal with only a small amount of solid crystals present. As the water content is reduced, for example by exposure to a low humidity environment, more of the solid crystal phase is found. Further X-ray diffraction studies identified the location of specific lipids in the model layered structure. Triglycerides and squalene are found in the hydrophobic methyl layer, while fatty acids, cholesterol and ceramides are located between the fatty acid chains. Water uptake was significantly enhanced when extracted stratum corneum lipids or model lipids were combined with the delipidated corneocytes, compared with water uptake of the lipids or delipidated corneocytes alone. Water uptake of the combined system was similar to that of isolated, intact stratum corneum. We determined the effect of glycerol, a well known skin moisturizer, on the model. While glycerol did not alter the water loss of the model at low relative humidity (6% RH), it maintained the liquid crystalline state of the lipid at the extreme condition; in the absence of glycerol the model showed substantial crystallization and exhibited multiple phases at 6% RH. Glycerol did not exhibit humectant behavior under these conditions. This study suggests that an alternate mechanism for moisturization may be to maintain the liquid crystalline structure under dry environmental conditions. Future studies using the model will examine the role of specific lipids and proteins in enhancing barrier properties; parameters measured will be phase behavior, water uptake/loss and alterations in diffraction patterns under different environmental conditions. Additives will be sought that improve the moisturization capacity of skin by altering biophysical properties of the lipid.