Ultraviolet (UV) irradiation causes changes in mechanical property and surface property of human hair. These changes of hair fiber can be more significant especially in bleached hair, and affects tactile sensation during combing or handling. In this study, changes in bending properties of bleached and UV-irradiated hair were evaluated. Bending stiffness of bleached hair was larger than that of untreated hair, and was increased further by UV-irradiation. By FT-IR measurement, it was found that bleaching and UV-irradiation caused oxidative scission of disulfide bonds in keratin, and that a-helix structure increased relatively. Based on these results, the mechanism of change in bending property and microscopic structure caused by oxidation stress was discussed. It was considered that deterioration in the mechanical property and chemical structure induced by UV irradiation was promoted with the bleached hair, because of ROS formation by residual hydrogen peroxide and decrease in the defensive function against oxidative stress.
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