392 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS =. Treated Untreated 30 o o-- o o 10 I Before Occlusion Affer Occlusion Figure 6. Capacitance measurements taken from dry skin after chronic treatment with a skin lotion T = treated sites, U = untreated control sites. The bars represent standard error. thickening of corneocytes located at levels as deep as those adjacent to the granular layer. The effect was attributed by the authors to swelling caused by higher levels of hydration. The technique used in the present study allowed us to observe a sizable decrease in the rate of water diffusion in dry skin chronically treated with a lotion, in agreement with the effects observed by others as described above. A possible mechanism accounting for the effect of the treatment is the formation of a substantive lipid barrier within the most superficial layers of stratum corneum. This possibility is supported by experi- ments which show that lipidic compounds, some of which are commonly used in skin lotions, are substantive to the stratum corneum (18), and they produce a positive effect on both the diffusional resistance (19,20) and the electrical capacitance of skin (1,3). CONCLUSION This report describes a sensitive method for measuring relative rates of water diffusion at the surface of the skin. The rate is indicated by changes in electrical capacitance as endogenous water accumulates in the outermost layers of the skin subsequent to occlusion with a thin layer of petrolatum. The diffusion rate is higher in subjects with dry skin than in those with normal skin. Application of a moisturizing lotion containing glycerine and mineral oil restored the skin to a normal-like condition with respect to its water-barrier function.

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