384 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS in conformance with Fick's law of passive diffusion, which when applied to this case implies that the lower the hydration within the surface layers of stratum corneum, the greater the rate at which water from deeper levels diffuses towards such drier regions. We also attempted to analyze the effects of the respective solvent exposure by employing a wet electrode and evaporimetry. However, in our hands these techniques yielded far less conclusive data on an equivalent number of sites. Therefore, it was considered that the dry electrode measurements, as described in this paper, may constitute an expedient method for investigating phenomena related to the presence of superficial skin dryness. There is considerable evidence that cosmetically dry skin [a condition categorized in a recent review by Kligman et al. (5) as xerosis vulgaris] is associated with higher electrical impedance when measured with dry electrodes (2) and increased rates of transepidermal water diffusion (TEW) as determined by evaporimetric measurements (6). Thus, the impedance and TEW characteristics in cosmetically dry skin show an apparent analogy with those observed in the solvent-dried skin. Based on this analogy, we decided that the technique used by us to observe the effects of solvent treatment may also be applicable to study similar parameters in dry skin. The present investigation was conducted in an attempt to: (a) observe differences between the electrical properties of normal and dry skin (b) relate the differences to the water barrier characteristics in the two skin types and (c) assess the effects of chronic treatment with a lotion on the water barrier properties of dry skin. MATERIALS AND METHODS INSTRUMENTATION The test electrode employed in the study was a vacuum controlled metal probe (Bor-Tru Inc., W. Redding, CT) constructed and used as described elsewhere (1). The main characteristics of this electrode are that the pressure exerted by it against the skin can be accurately controlled, and that with brief applications (fifteen to thirty seconds) it does not significantly alter existing levels of skin hydration. The reference electrode, a strip of aluminum foil folded to eliminate sharp edges, is held by the subject between the tongue and the palate. Both the characteristics of the test electrode and the placement of the reference electrode in contact with the oral mucosa (in which the resistance is relatively low and constant) contribute to a high degree of reproducibility, thus solving one of the problems associated with electrical measurements of skin in vivo. A Hewlett-Packard © (Model 4262a) capacitance-resistance meter generating 1.5 volts across the terminals and set to a frequency (f) of 100 Hz completed the circuit. The meter was interfaced with a Hewlett-Packard © Model 85 Microcomputer, which was programmed to control the meter and to calculate impedance (Z), phase angle (0), and capacitative reactance (Xc) from the primary resistance (R) and capacitance (C) values Z = 4R 2 + Xc 2, 0 = cotan Xc/R and X• = 1/(2 7r fC). The relationship of these parameters to the electrical properties of skin have been reviewed elsewhere (7,8).

ELECTROMETRIC ASSESSMENT OF SKIN DRYNESS 385 INSTRUMENT VALIDATION FOR MEASUREMENTS OF SKIN CAPACITANCE For reasons which will be discussed below, the data in this report were calculated on the basis of capacitance measurements. Due to the fact that the electrical bridge employed by us was not especially designed for skin research [unlike those used in other laboratories (2,8)], the capacitative nature of the measurements obtained with it had to be verified experimentally. The following procedure was used for that purpose. Six circular areas (3.8 cm 2 each) located on the inner forearms of one subject were treated with 5 •tl of an aqueous solution containing 1% Triton X 100 © (a surface active agent) and glycerine in one of the following concentrations expressed as percentages: 1, 2, 3, 4, 5 and 6 (W/W). This treatment has been shown (1) to produce a wide range of relatively stable skin hydration levels. After two hours of equilibration in an air conditioned room (T = 22øC, RH -- 55%) with subject idle and the forearms exposed, routine capacitance measurements were taken from the sites as described above. Then, the measurements were repeated with the test leads connected "in parallel" and "in series" with an external reference capacitor (capacitance decade box, Comell-Dubilier Electronics © No. Carolina 27526). Each time before these measurements were taken, the value of the reference capacitor was set to match to the nearest digit those obtained in the routine determinations. The two sets of the assumed skin capacitance readings, one obtained with the instrument alone and the other with the instrument connected to the external reference capacitor, were tested for conformance with summation rules applicable to ideal capacitors (details are given in the results section). SELECTION OF SUBJECTS WITH NORMAL AND DRY SKIN The studies were performed during February and March when the incidence of skin dryness is known (10) to be at maximum in the temperate zone. The subjects (n -- 27) were healthy male and female volunteers of twenty-one to fifty-seven years of age (mean = 40.5). Twenty individuals claimed to have dry skin on their extremities and used a moisturizer either during the winter or throughout the year seven regarded their skin as not dry and did not have to use lotions on their extremities. The subjects were instructed to wash their forearms exclusively with Ivory © soap daily and to refrain from using any topical products on the respective sites for seven days prior to the study. A last soap and water wash was done on day seven approximately three hours before the experimental steps described below. SUBJECTIVE EVALUATION OF SKIN DRYNESS AND ELECTROMETRIC EVALUATION OF TRANSEPIDERMAL WATER DIFFUSION On the day of testing the degree of dryness on the forearms was scored independently by two members of the laboratory staff on a scale of one (= absent or normal) to five (-- severe, marked by the presence of large scales and chapping). The scores were based on the degree of scaliness and superficial roughness evaluated visually by touch, and by the subjects' own perception. After completing the evaluation of dryness, three circular areas each of 3.8 cm 2 were delineated along the longitudinal axis of the inner forearms. After at least one hour of equilibration in an air conditioned room (T -- 22øC, RH -- 55%) in which the subjects sat idle with the forearms exposed, capacitance measure-