The effect of lipids, with and without humectant, on skin xerosis

Specialized lipids found in the stratum corneum, namely ceramides, have been shown to have beneficial skin properties due to their lipid bilayer-forming potential in the presence of cholesterol and fatty acids. We were interested in determining whether other bilayer-forming lipids, such as phospholipids, could deliver similar benefits and how these benefits compare with common moisturizer ingredients such as petrolatum and glycerol. We investigated a bilayer-forming mixture of phospholipids, cholesterol, and fatty acid for its effectiveness in treating soap-induced winter xerosis in double-blind, fully randomized clinical trials in which dryness on the dorsal aspect of the hands was visually assessed using a seven-point grading scale. Sixty-six healthy Caucasian women aged over 25 underwent a one-week soap "dry-down" and were treated for two weeks with twice-daily product applications in balanced treatment groups (N = 11). Treatments were compared statistically using repeated Wilcoxon rank sum tests (critical significance level of 5%). Examination of improvements in xerosis in vivo established that emulsions of phospholipids, cholesterol, and stearic acid alone, or thickened solutions of glycerol alone, did little to alleviate skin xerosis. When lipids and glycerol were combined, however, the emulsions acted in a synergistic way and reduced skin xerosis significantly and rapidly. In contrast, when phospholipids were replaced with petrolatum in the emulsions, the rate of xerosis alleviation was reduced, which implies that the bilayer-forming capabilities of phospholipids may be important in delivering optimal skin benefit. These studies demonstrate that lipids with bilayer-forming capabilities such as phospholipids can rapidly alleviate skin xerosis when combined with glycerol.