Internal Structural Changes in Age-Related Curved Hair Due to Cyclical Extension: An IR Spectroscopy Study

This study investigates the structural changes in age-related curved hair, known as "YUGAMI" hair, due to cyclical extension using infrared spectroscopy. The research involved stretching hair fibers at a strain level of 0.3-N for 500 cycles, with IR spectra collected every 25 cycles. The findings reveal that in age-related curved hair, the CH2 and C=O signals increased after 125 cycles, and the SO3H signal increased after 225 cycles, while no changes were observed in straight hair. The study identifies three steps in the internal transformation process: surface transfer of internal lipids, disulfide bond cleavage (C–S and S–S fission), and transformation of α-helices into β-structures after 225 stretches. These insights could inform hair care practices to manage curvature changes due to cyclical extension, such as daily grooming.