In vivo quantification of mechanical skin properties remains difficult. Several techniques have been developed, including tensile, torsional, indentation, suction, and vibration tests, which makes it difficult to compare results (37). The Cutometer® (Courage & Khazaka, Cologne, Germany) is a suction device, which applies a vacuum on the skin surface in a test area of only 3 mm2 by using a hand-held probe. The method is suitable to monitor therapy and/or progression of connective tissue diseases such as scleroderma, and has been used in cosmetology for efficacy quantification of antiaging products (38,39). When comparing the elasticity parameters of the forearm and the vulvar skin, the ratio between viscous deformation (Uv) and elastic deformation (Ue) and the biological elasticity, i.e., the ratio between immediate recovery (Ur) and total deformation (Uf), were both significantly lower in the vulvar than in the forearm skin. Age-related differences were similar on both sites (40). The fric-tional properties of the vulvar skin are of interest due to its relation to eventual frictional trauma and resulting lichenification. Using a Newcastle Friction Meter (Design Unit Department of Mechanical Engineering, Newcastle University, Newcastle-upon-Tyne, U.K.) with an annular Teflon ring rotating at constant velocity, the friction coefficient of the vulvar skin was found to be higher than on the forearm skin, due to higher hydration levels of vulvar stratum corneum (28).
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