Tribological testing of skin products: gender, age, and ethnicity on the volar forearm

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Abstract
Background/purpose: Few studies have focused on the simultaneous measurement of the friction and electrical properties of skin. This work investigates the feasibility of using these measurements to differentiate between the effects of chemicals commonly applied to the skin. In addition, this study also compares the condition of the skin and its response to application of chemicals across gender, ethnicity, and age at the volar forearm. Method: Friction and electrical tests were performed on 59 healthy volunteers with the UMT Series Micro‐Tribometer (UMT). A 13‐mm‐diameter copper cylindrical friction/electrical probe was pressed onto the skin with a weight of 20 g and moved across the skin at a constant velocity of 0.4 mm/s. Each volunteer served as his or her own control. The friction and electrical impedance measurements were performed for polyvinylidene chloride occlusion and for the application of glycerin and petrolatum. Results: No differences were found across age, gender, or ethnicity at the volar forearm. Polyvinylidene chloride (PVDC) occlusion showed a small increase in the friction and a small decrease in the electrical impedance; petrolatum increased the friction by a greater amount but its effect on the impedance was comparable to PVDC occlusion; glycerin increased the friction by an amount comparable to petrolatum, but it decreased the impedance to a much greater degree than petrolatum or the PVDC occlusion. An amplitude/mean measurement of the friction curves of glycerin and petrolatum showed that glycerin has a significantly higher amplitude/mean than petrolatum. Conclusion: The properties of the volar forearm appear to be independent of age, gender, and ethnicity. Also, the simultaneous measurement of friction and electrical impedance was useful in differentiating between compounds administered to the skin.