Measurement of hydration in the stratum corneum with the MoistureMeter and comparison with the Corneometer

Background/purpose: MoistureMeter is a novel capacitive device for measuring the hydration of stratum corneum (SC). The capacitor 'plates' are formed by the probe material and the well-conducting epidermal-dermal skin layers, while the dry layer of SC acts as an 'insulator' of the capacitor. Due to this measurement principle, the measurement depth is not constant, but equal to the thickness of the dry layer of SC. The present study was undertaken to test the MoistureMeter SC-2 in an experimental setup simulating the uppermost skin structure. The sensitivity of the MoistureMeter was compared with a conventional device Corneometer CM 820 in eight healthy volunteers. Methods: The experimental setup consisted of a polyethene foil simulating SC and a mixture of cellulose and saline simulating the underlying skin layers with a high water content. The hydration of SC of volar forearm was measured in eight healthy volunteers both with the MoistureMeter SC-2 and Corneometer CM 820 after the application of three different skin formulations: base, base plus salt (2 wt% NaCl), base plus salt and glycerin (5 wt%). In the sorption-desorption test, the skin was wetted with a drop of water and the dehydration was followed with both devices for 2 min. Results: The test with the experimental setup agreed with the results predicted by the mathematical capacitance model. The hydration values of the MoistureMeter SC-2 and Corneometer CM 820 correlated well (R=0.75), but the relative range of readings with the MoistureMeter was approximately three times larger than with Corneometer. The MoistureMeter was insensitive for the salt (2 wt% NaCl) of the formulation and differentiated the hydration effect of glycerin better than the Corneometer. In the sorption-desorption test, the MoistureMeter demonstrated the individual differences between the volunteers, whereas with the Corneometer the differences were minimal. Conclusion: The capacitive measuring principle of the MoistureMeter was demonstrated in an experimental arrangement. Although both instruments yielded equivalent data with the base formulation, the MoistureMeter was a more sensitive device than the Corneometer CM 820 and independent of added salt in the formulations.