Stratum Corneum Dynamic Hydration Test

Abstract

To avoid traditional invasive biopsy, the observation of skin surface changes has been conducted to focus on the visually identifiable and palpable changes. However, there is a limit to such sensory evaluation method in normal looking skin. Recent developments have enabled us to perform even non-invasive in-situ evaluation of the superficial portion of the skin in vivo. We can now quickly and quantitatively evaluate the hydration state of the stratum corneum (SC) that determines the softness and smoothness of the skin surface by measuring high frequency conductance or capacitance of the skin. The dynamic hydration tests of the SC, namely sorption-desorption test (SDT), moisture accumulation test (MAT) and plastic occlusion stress test (POST), demonstrate the dynamic hydration changes induced either exogenously or endogenously in the SC using different artificial hydration procedures. By performing these tests, we can numerically assess the skin surface differences due to location, age or even minor skin changes induced by skin irritation or abnormal cornification. Moreover, with these methods, we can quantitatively evaluate the efficacy of various topical agents to soften and smoothen the skin surface. By employing such methodology, we can also follow the dynamic hydration changes occurring in the skin surface after application of topical agents such as skin care products or pharmaceutical agents, which enables us even to assess quantitatively their clinical or cosmetic efficacy within a few minutes.