Water sorption-desorption test of the skin in vivo for functional assessment of the stratum corneum.

Based on the evidence from our previous studies that we can evaluate the hydration state of the skin surface quickly and quantitatively in terms of conductance to the high frequency electric current of 3.5 MHz, we have established a simple in vivo function test that furnishes information on the hygroscopic property and water-holding capacity of the stratum corneum in a few minutes. The test procedure consists of electromeasurements before and after application of a droplet of water on the skin for 10 seconds to obtain data on the hygroscopic property of the skin surface and later serial measurements at an interval of 30 seconds for 2 min to evaluate the water-holding capacity. Under usual ambient conditions normal skin surface showed a high rise in conductance just after application of water, which was followed by a rapid fall-off within 30 seconds, thereafter by gradual return to the prehydration levels by 2 min. By this method we have demonstrated that (i) the superficial horny layer of normal skin is much less hygroscopic and less capable of holding water than the corresponding deeper portions and that (ii) scaly skin shows functional defects in both hygroscopicity and water-holding capacity, between which the former normalizes much faster than the latter.