Purpose: The objective is to determine the usefulness of cathepsin L (Cat L) activity derived from the stratum corneum as an index of skin conditions by comparing the cheek and the forearm, in 20 female young adults. Methods: The sebum quantity, hydration index, melanin index andpH were measured with a sensor system consisting of a sebumeter, a corneometer, a mexameter and a pH meter. The stratum corneum was collected using tape stripping. Cat L and total protein (TP) were analyzed and the Cat L/TP ratio was calculated. Results: Our results indicated that (i) chronic sun exposure causes an increase in Cat L activity; and (ii) in order to cancel out the influence of the collecting technique, it is very important to measure the Cat L/TP ratio. Conclusion: It is considered that the Cat L/TP ratio may be a useful index of the skin conditions in humans.
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