Characterization of Curved Hair of Japanese Women with Reference to Internal Structures and Amino Acid Composition

The study quantitatively investigated hair curvature in 230 Japanese women aged 10 to 70 years, finding that 53% had straight hair and 47% had curved hair, with curl radii ranging from 0.6 to 16 cm. Transmission electron microscopy (TEM) revealed an inhomogeneous internal structure in curved hair, with differences in amino acid composition between the outer and inner regions. These findings were similar to the differences observed between ortho- and paracortical cells in wool fibers, suggesting a universal structure for curved mammalian hair.