Characterization of curved hair of Japanese women with reference to internal structures and amino acid composition

The variation of hair curvature in Japanese women was quantitatively investigated and the structure of curved hair was characterized with transmission electron microscopy (TEM) and amino acid analysis. Two hundred and thirty Japanese women volunteers, aged from 10 to 70 years, were randomly selected. The evaluation of the volunteers' natural hair shape showed that 53% of Japanese women have straight hair, while the remaining 47% have curved hair (varying from a slightly wavy shape to a frizzy style). The average curl radius of the volunteers' hair was determined to be 4.4 +/- 2.3 cm, and ranged widely from 0.6 to 16 cm. The TEM observation of curved hair fiber revealed an inhomogenous internal structure between the outer and inner regions of the curved shape. In relation to the inhomogeneous structure of the curved hair, different amino acid composition of the hair keratin was observed between the outer and inner regions. Interestingly, these results of the TEM observation and the amino acid analysis are analogous to the difference between the ortho- and paracortical cells in wool fibers, suggesting the universal structure of curved mammalian hair.