Water Content of Stratum Corneum in Vivo

We have developed a method to measure the water content of the stratum corneum of intact skin. In its present form the technique is a transfer method. Like many other transfer measurements in medicine the technique is most accurate when individually calibrated with samples of the subjects own tissue. Electrical resistivity is accurately measured in vivo during the course of experimental procedures using a four-fingered microelectrode probe developed for this purpose. Calibration in vitro on samples taken from the same site is made by comparing resistivity vs. total water content measure gravimetrically. Differences in conduction properties of different samples are not now predictable, and can cause large estimate errors if a single calibration curve is used for all subjects. The transfer method eliminates this source of error. Present limitations on the accuracy of the transfer method arise from uncertainties in regional water distribution during calibrations. The method is restricted in theory to stratum corneum thicker than the spacing of the electrode fingers. With present electrodes this theoretical restriction limits the use to the palms and soles. Future empirical testing of these electrodes and the manufacture of smaller electrodes may permit application of the method to areas of thin stratum corneum as well.