Influence of exfoliating facial cleanser on the bio-tribological properties of human skin

In daily life, cosmetics can play important roles in facial skin moisturizing, whitening and sun protecting. Unfortunately, the aged skin stratum corneum (SC) often impedes the penetration for cosmetics. Regular removal of the extra aged horny cells can facilitate the penetration for cosmetics and improve the performance of the skin. However, no study has assessed the detailed effects of exfoliating facial cleanser on the friction properties of human skin and the degree of aged SC removal. In this paper, the effects of three kinds of scrub facial cleanser with different sizes, amounts and hardness scrub particles on the tribological properties of human skin have been investigated in vivo using a UMT-II tribometer under the simulated face washing conditions. The hardness of the scrub particles were measured by using a Nano-Hardness/Scratch Tester. The results showed that the aged SC has all been removed by the three kinds of scrub cleanser under the reciprocating sliding wear mode, which resulted in decrease of skin surface roughness and increase of skin conductance and hydration. Thus, the adhesion force and friction coefficient between the hydrated skin and a probe increased due to the increased contact area and skin hydration. Compared with the other two cleansers, the cleanser with two kinds of size and moderate hardness scrub particles made the skin to deform more elastically and removed more aged SC, which led to greater decrease in skin surface roughness and greater increase in skin conductance, hydration and adhesion. Hence the skin friction coefficient and penetration were higher and the moisturizing persistence lasted longer time after the same moisturizer was used. This indicated that the properties of scrub particles in cleanser played important roles in skin tribological behavior and penetration. The results may be instrumental in developing and testing skin cosmetics.