Analysis of structural changes in bleached keratin fibers (black and white human hair) using Raman spectroscopy

To investigate the influence of bleaching treatments on keratin fibers, the structure of cross-sections at various depths of bleached human hair (black and white human hair) was directly analyzed without isolating the cuticle and cortex, using Raman spectroscopy. The S-S band intensity existing from the cuticle region to the center of cortex region of virgin white human hair decreased, while the S-O band intensity at 1040 cm(-1), assigned to cysteic acid, increased by performing the bleaching treatment. Especially, the S-O band intensity of the cuticle region increased remarkably compared with that of the cortex region. Also, the amide III (unordered) band intensity in the cortex region increased, indicating that some of the proteins existing throughout the cortex region changed to the random coil form. Moreover, it has been found that the S-S band intensity existing from the cuticle region to the center of the cortex region of the virgin black human hair decreased remarkably, while the S-O band intensity increased significantly compared with that of the virgin white human hair by performing the bleaching treatment. From these experiments, we concluded that the melanin granules including metal ions act as a decomposition accelerator for the oxidizing agent, thereby leading to a higher level of disulfide (-SS-) group cleavage in the black human hair compared with that of the white human hair.