j. Soc. Cosmet. Chem., 32, 421-435 (December 1981) In vivo evaluation of skin lotions by electrical capacitance: II. Evaluation of moisturized skin using an improved dry electrode G. P. SERBAN, $. M. HENRY, V. F. COTTY and A.D. MARCUS, Bristol-Myers Products, 225 Long Ave., Hillside, NJ 07207. Received May 22, 1981. Synopsis An improved type of DRY ELECTRODE was used to evaluate the levels of SKIN HYDRATION following application of several LOTIONS or selected ingredients. The main characteristics of this electrode are that (a) it allows repeated measurements from the same sites without changing existing moisture levels and (b) the contact pressure against the skin surface can be made constant. The electrode was found to be more sensitive in detecting differences between normal and experimentally induced dry skin than a silver chloride electrode filled with an electrolyte paste. Evidence is presented that some moisturizers retain hydrating activity after the skin sites treated with these are thoroughly washed with soap and water. INTRODUCTION The presence of water in the stratum corneum (SC) is related to important characteris- tics of this tissue (1, 2) and electrical measurements have become useful in assessing its degree of hydration (3, 4, 5, 27). In a review of the instrumental techniques for in vivo evaluation of moisturization Pugliese (6) referred to the controversy over the use of dry or wet electrodes when measuring impedance (Z). Clar, et al. (3) indicate that the major problems when using dry electrodes are electrode polarization and the accumulation of moisture under the electrodes. Another problem with dry as well as with wet electrodes is that the measurements are affected by the amount of pressure with which the electrodes are applied to the skin, thus increasing variability. This report describes a novel, dry electrode which overcomes the above problems and permits evaluation of moisturizers by electrical parameters without the need for an electrolyte in contact with the skin. Further, it compares the moisturizing efficiency of several formulations and provides data indicating that the hydration of the SC may continue for some time following removal of a moisturizer. This work was done using a non-conventional experimental design and electrode placement. 421

422 .JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS EXPERIMENTAL A. INSTRUMENTATION A Wayne-Kerr (8331) autobalance precision-bridge, operating at a fixed frequency of 1592 Hertz, coupled with a two-pen recorder, was used for the conductance and capacitance measurements. B. ELECTRODE DESIGN AND PLACEMENT A wire-mesh dry electrode (Figure 1) was constructed from a piece of copper tubing. The end of the tubing that was to come in contact with the skin was closed using a FT ..•CT 40 mm - WM = WIRE MESH CT = COPPER TUBING TL = TEST LEAD FT = FLEXIBLE TUBING RS = RUBBER STOPPER TC = TUBING CONNECTOR WM ß ,•__'5- - -" • - Figure 1. Schematic of prototype wire mesh, vacuum electrode for electrical conductance and capacitance measurements on skin. stainless steel wire-mesh (diameter of wire = 0.0940 mm, width of opening = 0.1168 mm, open area = 30.7%, Newark, NJ Wire Cloth Co., Code ZZM). The other end was connected to a low power vacuum pump (maximum vacuum 27 in. Hg., Ace Scientific, Cat. No. 21-4489-01) with a soft rubber tubing (approximate length 0.7 m.): During the measurements, the reference electrode (a three-inch strip of aluminum foil folded to eliminate sharp edges) was placed in the mouth and the subjects were asked to hold it between the tongue and the palate. After turning on the vacuum pump, the wire-mesh electrode was placed vertically over the test area where it was held manually for 15 seconds. Under these conditions, very little if any variation occurs in the conductance or capacitance readings as a result of electrode or subject movement. (see Figure 4). For the wet electrode measurements a Beckman Standard (Cat. No. 217413) silver chloride electrode filled with a potassium chloride electrode cream (EC2, Grass Instruments Company, Mass.) was used. The electrode placement was the same as described above but no attempts were made to standardize the pressure against the skin. The readings were taken directly from the bridge 30 seconds after electrode placement.