Dopamine-polymerized macromolecules for rapid and safe hair dyeing

This study addresses the limitations of synthetic hair dyes, such as potential carcinogenicity and allergies, and the drawbacks of conventional natural dyes, like long treatment times. The research proposes a safe and efficient hair dyeing system using dopamine (DA) and genipin (GP). When applied together, DA and GP undergo rapid self-assembly and cross-linking to coat hair, turning it black within 40 min without additives such as mordants or adhesives. The dyeing speed and color intensity can be controlled by adjusting the GP concentration. Evaluations using SEM, UV–Vis, and ATR–FTIR spectroscopy confirmed effective morphological changes, while MTT assays demonstrated low toxicity. Furthermore, the dyed hair exhibited high durability, maintaining its color even after dozens of shampooing cycles. This DA/GP dye system provides a promising natural alternative for rapid, safe, and long-lasting hair coloring.