The Secrets of Beautiful Hair: Why Is It Flexible and Elastic?

The study investigated the flexible and elastic properties of hair fibers using untreated hair from 50 Japanese female volunteers and untreated Caucasian hair. Researchers found that hair's composite structure, including the cortex with intermediate filaments and keratin-associated proteins, contributed to its mechanical properties. They developed a treatment with succinic acid that improved hair's flexibility and elasticity, making it more resilient and enhancing its appearance. The study revealed that flexible/elastic hair had a concentric double-layered distribution of cortical cells, while inflexible/inelastic hair had a dispersed pattern. Damage increased outer layer stiffness, but succinic acid treatment selectively softened it, improving flexibility and elasticity. A three-step treatment system with succinic acid was effective for both Japanese and Caucasian hair, showing perceived improvements in softness, bounce, flexibility, and elasticity.