Affiliations: Innovative Beauty Science Laboratory, Kanebo Cosmetics
Inc., Kotobuki-cho, Odawara-shi, Kanagawa, Japan | Skincare Research Laboratory, Kanebo Cosmetics Inc.,
Kotobuki-cho, Odawara-shi, Kanagawa, Japan | Photon Factory, Institute of Materials Structure
Science, High Energy Accelerator Research Organization, Tsukuba-shi, Ibaraki,
Japan | Advanced Research Institute for Science and
Engineering, Waseda University, Shinjuku-ku, Tokyo, Japan | Department of Nuclear Engineering, School of
Engineering, Tokai University, Kitakaname, Hiratsuka-shi, Kanagawa, Japan
Abstract: Human hair fibers are primarily composed of keratin protein,
characterized by a very high content of cysteine, a sulfur-containing amino
acid, which ordinarily forms cystine via a disulfide bond. It is known that
some cystine residues are converted to cysteic acid during permanent waving or
hair coloring, although details of their distribution and extent are still
unclear. In this study, by using difference in XANES profiles of cystine and
cysteic acid at the S-K absorption edge, the formation of cysteic acid was
confirmed for homogenized samples of permed or bleached hair. Furthermore
chemical mapping of cysteic acid was performed on hair-section samples with
X-ray contact microscopy. The peripheral region, cuticle, in bleached hair
showed the highest content of cysteic acid compared with the other parts, while
permed hair showed relatively uniform distribution. This finding suggests that
perming and bleaching damage hair by different mechanisms.
