Friction and wear studies of human hair and skin

Characterization of friction and wear properties of hair and skin is essential to develop better shampoo and conditioner products and advance biological and cosmetic science. Literature on the tribological characterization of hair and skin is scarce to date. In this study, friction experiments were performed at a range of loads, speeds, and skin area in order to study their effect on skin–hair contact. In addition, friction and wear experiments were performed to simulate skin–hair and hair–hair contacts at nominal conditions. Environmental dependence of hair friction is of importance and the effects of temperature and humidity on the friction of hair against skin were studied. Measurements were made using a flat-on-flat tribometer under reciprocating motion on Caucasian, Asian, and African hair (virgin, chemo-mechanically damaged, and conditioner treated) against polyurethane film (synthetic skin) and against hair. The morphology of hair and skin were measured by atomic force microscopy (AFM) and optical microscopy. Average coefficient of friction values were measured for each ethnicity and hair type, and are discussed. The directionality dependence of friction with respect to hair is also discussed.