Evaluation of Cysteic Acid in Bleached Hair Using Infrared Spectroscopy

The study evaluated cysteic acid generation in bleached human hair using infrared spectroscopy. Results indicated that cysteic acid levels increased linearly with the square root of bleaching time, suggesting a diffusion-controlled reaction. This behavior was observed in both the cuticles and cortex of the hair, with higher disulfide crosslink density and slower hydrogen peroxide diffusion rates in the A-layer and exocuticle. Infrared microscopic measurements confirmed even cysteic acid distribution within the cortex, implying that hydrogen peroxide diffusion from the cell membrane complex into cortical cells controlled cysteic acid generation.