Background: Although effective moisturizers can improve xerotic skin changes immediately, their effects are only transient, because the materials applied to the stratum corneum (SC) are easily shed from the skin surface by the daily desquamation process. However, there are a few lines of clinical as well as experimental evidence suggesting that, once application of effective moisturizers is repeated daily, they may produce persistent effects without being influenced by the desquamation of the skin surface. If we can expect such pharmacological effects by simple repeated applications of moisturizers on the skin surface, it will provide a great motivation for the introduction of corneotherapy into the treatment of xerotic skin problems. Objective: This study was designed not only to confirm the feasibility of corneotherapy but to propose a practical method to assess such long-lasting effects of moisturizers by using biophysical methods. Methods: We conducted applications of various moisturizers twice daily to different areas of the flexor surface of the forearms for the initial 5 days of the first week. Thereafter, we performed biophysical measurements of the SC of these areas in the second week, namely 3, 5 and 7 days after their last applications. Results: Daily repeated applications of moisturizers did not induce any change in the water barrier function of the SC or in the size of desquamating corneocytes, a parameter for turnover rate of the SC. However, they substantially increased high-frequency conductance, a parameter for the hydration state of the skin surface, for several days in both normal individuals and patients with atopic xerosis, although the lasting effects were shorter in the latter. The obtained data enabled us to rank the efficacy of moisturizers either according to the duration of the lasting effects or the magnitude of an increase in the hydration levels of the SC. Conclusion: The present results confirmed the feasibility of corneotherapy, in which even simple application of moisturizers targeted at the SC can produce unexpected persistent clinical effects after their repeated treatments. The method described in this study constitutes a practical assay system to evaluate the efficacy of topical agents used for dry skin problems objectively and quantitatively.

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