Effect of Oxidation Stress on the Mechanical Property of Human Hair

The tactile sensation of human hair during combing by finger or brush is deteriorated by damages induced by external stimuli, such as UV irradiation or bleaching. It is because the characteristics of human hair are affected by external environments. It is reported that the damage on human hair by UV irradiation is accelerated in bleached hair. In this study, changes in physical property of bleached and UV-irradiated hair were examined. Bending stiffness of bleached hair was larger than that of normal hair, and was increased further by UV irradiation. The results of FT-IR measurement showed that the bleach treatment and subsequent UV irradiation induces the S–S bond scission which causes elution or denaturation of amorphous matrix in the cortex layer. Elution of matrix protein causes decrease in water retention capacity, which decreases the flexibility of hair fibre. It was considered that the change in chemical structure induced by UV irradiation was more accelerated in the bleached hair, because reactive oxygen species is generated by residual hydrogen peroxide which causes the oxidative damage.