Background/aims: The research on the treatment of "dry skin syndrome" is hampered by the lack of a suitable animal model. Previously, we developed a validated guinea pig in vivo model in which the dry skin syndrome persists for at least one week. This model allows us to compare the pharmacological effectiveness of known and potential moisturizers for the treatment of dry skin syndrome. Our aim is to study whether the moisturizing efficiency of humectants depends on the solvents in which they are dissolved.
Methods: "Dry skin syndrome" was induced on the shaved skin of one side of guinea pigs by daily application of 2% sodium lauryl sulphate in deionized water (SLS) for three days. The other shaved side was used as a control. After confirming skin dryness, the affected side was treated for six days with glycerol or 1,2-hexanediol dissolved in different solvents, including water, medium-chain triglycerides (MCT), or mixtures of MCT with isopropyl alcohol in various proportions. The in vivo moisturizing effect was measured using a Corneometer CM 825A, and erythema was assessed with a Mexameter MX 16A.
Results: Treatment with glycerol (1M) in water reversed skin dryness as measured by both instruments. However, no moisturizing effect was observed when glycerol was dissolved in MCT, likely because glycerol does not dissolve in the oil. Similarly, no moisturizing effect was found with glycerol in mixtures of MCT and isopropyl alcohol, nor with 1,2-hexanediol (1M) dissolved in MCT oil. Glycerol and 1,2-hexanediol only reduced erythema when dissolved in water.
Conclusion: Polyol moisturizers such as glycerol or 1,2-hexanediol do not act effectively in the presence of oils against sodium lauryl sulphate-induced dry skin in our guinea pig model. Given that in an oil-in-water (O/W) emulsion the water evaporates within minutes, the ability of moisturizing emulsions to treat dry skin is questionable. Conclusions about the moisturizing efficiency of a preparation cannot be drawn solely from the presence of humectants; the effect of the finished preparation must be studied.
Keywords: dry skin syndrome, guinea pig, humectant, efficiency
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