Structural Analysis of Macrofibrils in a Human Permanent Waved Hair by Scanning Microbeam Small-Angle X-ray Scattering Measurements

It has been experimentally shown that hair subjected to permanent wave treatment quickly changes into uncurled hair during daily hair-care activities. However, the mechanism of curl fallout has not been clarified. In previous studies, the relationship between permanent wave treatment and disulfide bonds in hair has been studied. Because permed hair falls out its waves without any chemical treatment, we focused on the hair microstructure rather than the disulfide bonds. To examine the relationship between the hair curl shape and the intermediate filament (IF) organization in hairs, scanning microbeam small-angle X-ray scattering measurements were performed. It was found that in permed hairs, the IF orientation on the convex side of the curvature was different from that on the concave side. By contrast, for permed hairs with curl fallout, the IF orientation on the convex curvature side was not significantly different from that on the concave side. Our findings suggest that the curl shape of permed hairs is related to its anisotropic IF orientation between the convex and concave side of the curl, and control of this IF orientation will allow for effective reduction of curl fallout.