Characteristic Microstructure of Curved Human Hair

In the 2009 study on the microstructure of curved human hair, researchers discovered asymmetrical structures and compositions between the convex and concave sides of the hair. The convex side exhibited faster permeation for fluorescein isothiocyanate, smaller and more dispersed macrofibrils, a spiral arrangement of intermediate filaments, and higher levels of acidic amino acids and glycine. Conversely, the concave side had larger, fused macrofibrils, intermediate filaments aligned parallel to the hair axis, and higher levels of cysteine. These structural and compositional differences may contribute to the curved shape of hair and are similar to the characteristics found in wool, indicating a possible commonality in the structure of curved hair across mammals.