Imaging of Photo-Damaged Hair with a Differential Phase Scanning X-Ray Microscopy

In recent years, hair damage by sunlight and chemical treatment such as perming and bleaching has become a consumer concern. It is important to understand the effect of sunlight and chemical treatment on hair microstructure to develop the technology for protection and repair of hair. Our previous study demonstrated that a differential phase contrast scanning X-ray microscopy was a useful nondestructive analysis method to observe internal hair structure with high-resolution. In this study, hair samples with three different chemical treatment （ normal, perming and bleaching ） and additional irradiation by artificial sunlight were observed with a scanning X-ray microscopic tomography system using a synchrotron radiation light source in order to understand the damag-ing effect of both sunlight and chemical treatment on hair. The porosity rate in the cortex is higher in the permed hair than normal hair and void distribution in the cross section of permed hair is localized. The porosity rate in the cortex of permed hair is decreased by additional irradiation. The porosity rate of bleached hair is the same as that of normal hair and isn ʼ t changed by the irradiation. These results suggest that hair microstructural change in the cortex by sunlight is affected by the prior chemical treatments, and development of varied protection and repair technology de-pending on the prior treatment situation is needed.