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.

A closed unventilated chamber for the measurement of transepidermal water loss.

BACKGROUND/AIMS: Open chamber systems for measuring transepidermal water loss (TEWL) have limitations related to ambient and body-induced airflows near the probe, probe size, measurement sites and angles, and measurement range. The aim of the present investigation was to develop a closed chamber system for the TEWL measurement without significant blocking of normal evaporation through the skin. Additionally, in order to use the evaporimeter to measure evaporation rates through other biological and non-biological specimens and in the field applications, a small portable, battery-operated device was a design criteria. METHODS: A closed unventilated chamber (inner volume 2.0 cm(3) was constructed. For the skin measurement, the chamber with one side open (open surface area 1.0 cm(2) is placed on the skin. The skin application time was investigated at low and high evaporation rates in order to assess the blocking effect of the chamber on normal evaporation. From the rising linear part of the relative humidity (RH) in the chamber the slope was registered. The slope was calibrated into a TEWL value by evaporating water at different temperatures and measuring the water loss of heated samples with a laboratory scale. The closed chamber evaporation technique was compared with a conventional evaporimeter based on an open chamber method (DermaLab), Cortex Technology, Hadsund, Denmark). The reproducibility of the closed chamber method was measured with the water samples and with volar forearm and palm of the hand in 10 healthy volunteers. RESULTS: The skin application time varied between 7 and 9 s and the linear slope region between 3 and 5 s at the evaporation rates of 3-220 g/m(2) h. A correlation coefficient between the TEWL value from the closed chamber measurements and the readings of the laboratory scale was 0.99 (P < 0.001). The reproducibility of the evaporation measurements with the water samples was 4.0% at the evaporation rate of 40 g/m(2) h. A correlation coefficient of the TEWL values between the closed chamber and open chamber measurements was 0.99 (P < 0.001) in the range where the response of a conventional evaporimeter was linear (until 120 g/m(2)h. With volar forearm and palm of the hand of 10 healthy volunteers the reproducibility of the measurements was 8.0 and 10.1%. CONCLUSION: The closed chamber technique solves the drawbacks related to open chamber evaporimeters. Especially, it extends the measurement range to high evaporation rates and TEWL measurements can be performed practically at any anatomical sites and measurement angle. By the use of a closed chamber the disturbance related to external or body-induced air flows on the measurement can be avoided.