Reproduction Mechanism of Disulfide Cross-Links in Permed Hair by Washing After Reduction with Thioglycolic Acid

The study investigated the reproduction of disulfide (SS) cross-links in permed hair during the washing step after reduction with thioglycolic acid (TGA) and subsequent oxidation by sodium bromate. The researchers aimed to quantify the reformation of SS cross-links and understand the effect of washing time on hair's microstructure. They analyzed the force-extension curve of rubber-like swollen hair fibers using rubber elasticity theory. The findings indicated that while the SS cross-linked structure of intermediate filament (IF) proteins remained intact, the intermolecular SS cross-links between keratin-associated proteins (KAP) were regenerated during washing, leading to increased extension modulus and breaking stress of the hair fibers in water.