The inherent capacitance of moisturising creams: A source of false positive results?

The capacitance is a frequently used measurement of skin hydration in vivo, therefore any potential for false capacitance results is of importance. This in vitro study is to investigate the capacities of moisturising creams to cause false positive results. Adding different volumes of demineralised water and saline on dry clean plastic-backed tissue paper and measuring the capacitance values, the standard relation curve of capacitance value and volume of water was established. Four moisturising creams, petrolatum, a protective cream and a gel were then applied to the same kind of tissue paper in constant volumes, and were measured for weights and capacitance values over a 1-hour period allowing the gradual evaporation of water and volatile elements. A positive linear relation-ship was found between volume of water and capacitance value. All the creams had inherent capacitance that correlated with their water content. The inherent capacitance of creams decreased over time and ultimately reached comparable low values. The decrease in capacitance correlated significantly with weight reduction, except for petrolatum, which showed negligible inherent capacitance and weight reduction. The rates of decrease in capacitance value versus cream weight were significantly different for different creams. The results assured that capacitance value correlates to water content, and the inherent capacitance of creams may contribute to false positive skin capacitance in vivo if measured before water and other volatile elements of creams evaporate from the skin surface. In addition, the inherent capacitance and its durability may be relevant characteristics for further comparative studies of moisturisers and their clinical efficacy. Copyright (C) 2000 S. Karger AG, Basel.