A highly resistant structure between the cuticle and the cortex of human hair III: Characterzation of the structure CARB

Abstract

It was previously reported that a highly resistant structure, which functions as a barrier against the penetration of dyes, is present at the interface between the cuticle and the cortex of human hair. That structure was named CARB, cuticle anchored resistant base. The goal of this study was to clarify the formation and composition of the structure CARB. Cuticular substructures were observed from the keratinized area of each hair to its root end. The positions where the CARB structure appeared were isolated, and the barrier ability before and after that structure was evaluated. The distributions of glycolipid and cystine were measured using a nano-IR and a transmission electron microscope (TEM). Cuticular substructures were fully constructed several mm from the hair bulb of the hairs observed. The results show that keratinization at the distal side of the cuticle cell precedes that of the proximal side, and CARB is fully constructed last among the substructures. Glycolipid was preferentially distributed at CARB in the keratinized area. The cystine content of CARB is lower than that of the A-layer; however, it is slightly higher than that of the exocuticle and the inner layer. These results demonstrate that CARB is produced in the final stage of keratinization of the cuticle layers. The rich contents of glycolipid and cystine might contribute to its resistant property.