390 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS dry stratum corneum in vitro changes with hydration from 2-3 to about 600. Kraning et al. (13) also report an increase in K after hydration of skin in vivo. The direct relationship between C and K can be observed from the following simplified equation: C = KA/[47rD(9 x 10n)]Farads, in which A is the plate area, D is the difference between plates and 9 x i0 n is a constant. It has been reported by several investigators (1,2,3) that C and the reciprocal of R correlate closely when measuring superficial skin hydration. On this basis it would appear that either C or R and Z or 0 which can be calculated from the former two (refer to methods section) would be equally suitable for determinations of WDi as described herein. However, for several reasons the main results in this report are based on C measurements. Work in this laboratory (manuscript in preparation) shows that the signal to noise ratio is higher for C than for R when measuring changes in the hydration of the corneal matrix. We also observe that along with the higher sensitivity, C is less dependent on phenomena related to skin galvanic response (SGR) induced by the activation of sweat glands. The latter can constitute a source of error consequently, its effects on the measurements must be reduced as much as possible (9,11). An additional reason for employing C measurements is based on work by Clausen, et aL (14). Their data show WDi 20 IS 10 0 Treated Untreated Figure 5. The effect of chronic treatment with a skin lotion on the WDi of dry skin. Note that before the measurements were taken the sites were thoroughly washed with soap and water and allowed to equilibrate with the environment. The bars represent standard error.

ELECTROMETRIC ASSESSMENT OF SKIN DRYNESS 391 that C is a more sensitive indicator of the size of the effective area under the electrode particularly when R is very low. Since one of the objectives of the present work was to observe differences between normal and dry skin in which, due to topographical characteristics, the ratio of nominal to effective area is different (15), C appeared to be the logical parameter of choice. The properties of stratum corneum with respect to its water barrier function have both medical (2) and cosmetic (12) implications. The technique described in this paper is useful for demonstrating that skin which manifests signs of superficial dryness permits water to diffuse to the exterior at a higher rate than does normal skin. Similar but somewhat less conclusive results have been reported by Leveque et al. (6) based on measurements of transepidermal water loss. The increased rate of water diffusion detected at the surface of dry skin by means of C measurements could be accounted for by one or a combination of the following factors: (a) A higher ratio of actual to apparent surface area known to exist in dry skin (15), possibly in relation to an error of desquamation (5). (b) A partial lack in the ability of the most superficial layers of stratum corneum to prevent loss of water (which with this technique is measured as it accumulates at the skin-petrolatum interface). (c) An increase in the permeability of stratum corneum perhaps throughout its entire thickness. More experimental data would be needed in order to analyze the contributions of these factors to the observed differences. EFFECT OF TREATMENT WITH A SKIN LOTION ON THE TRANSEPIDERMAL WATER DIFFUSION OF DRY SKIN Figure 5 shows the effect of treatment with lotion on the WDi values of dry skin. A comparison between the values presented in this figure and those given in Figure 3 reveals that the WDi values in dry skin after treatment with lotion are very close to those measured in normal skin. In addition to a lower WDi, the treated sites have a slightly higher capacitance (P -- 0.01) than the control sites (Figure 6). This indicates greater hydration of the stratum corneum. Furthermore, after occlusion with petrola- turn (Figure 6), the rate at which water diffuses to the skin surface is lower in the treated than in the untreated sites (P = 0.005). The two effects (higher initial levels of hydration and decreased rate of hydration with occlusion in the treated sites) are consistent with one another and, although not measured with the same sensitivity, demonstrate a favorable change in the water barrier properties of stratum corneum. Several studies suggested to us indirectly that chronic occlusion with a moisturizing lotion may result in an improvement of the water barrier function of stratum corneum, and that we may be able to observe the effect using WDi measurements. Studies by Kligman (10) show that treatment of xerotic skin with petrolatum produced a favorable and lasting change in the skin topography. Other experiments (16) appear to demonstrate a cause-effect relation between chronic treatment with a lotion and an improvement in the water sorption properties of stratum corneum. More recently, transmission electron micrographs revealed (17) that regular use of a lotion resulted in