Coefficient of friction: tribological studies in man – an overview


Howard I. Maibach
Department of Dermatology
School of Medicine
University of California
San Francisco
Box 0989
Surge 110
San Francisco
CA, 94143-0989
Tel: 415 476 2468
Fax: 415 753 5304


Background/purpose: Compared to other studies of skin, relatively few studies have focused on the friction of skin. This work reviews existing skin friction, emphasizing test apparatuses and parameters that have added to information regarding the friction coefficient. This review also outlines what factors are important to consider in future friction studies.

Methods: Past studies have utilized numerous designs for a test apparatus, including probe geometry and material, as well as various probe motions (rotational vs. linear). Most tests were performed in vivo; a few were performed in vitro and on porcine skin.

Results: Differences in probe material, geometry and smoothness affect friction coefficient measurements. An increase in skin hydration, either through water or through moisturizer application, increases its friction coefficient; a decrease in skin hydration, either through clinical dermatitis or through alcohol addition, decreases the coefficient. Differences are present between anatomical sites. Conflicting results are found regarding age and no differences are apparent as a result of gender or race.

Conclusion: Skin friction appears to be dependent on several factors – such as age, anatomical site and skin hydration. The choice of the probe and the test apparatus also influence the measurement.