Quantifying the Effects of Repeated Dyeing: Morphological, Mechanical, and Chemical Changes in Human Hair Fibers

This study examines the effects of repeated hair dyeing on human hair fibers, focusing on morphological, mechanical, and chemical changes. It finds that even a single dyeing session causes noticeable damage, with significant deterioration after three or more treatments. Dyeing reduces cuticle step height, increases surface roughness, and alters protein structure, leading to increased hair stiffness and reduced water content. While mechanical properties and protein composition change non-linearly, nanoscale damage to the cuticle surface increases proportionally with dyeing sessions. The study emphasizes the importance of considering the effects of dyeing on hair health and suggests further research on diverse populations.