Permanent Low-Toxicity Hair Dye Based on Pregrafting Melanin with Cystine

A pregrafting strategy is presented to construct covalent bridges between synthetic melanin, i.e., polydopamine (PDA), and hair for permanent hair dyeing. As a result, PDA is more uniformly distributed throughout the hair surface, and the dyed hair shows higher color intensity and better durability to washing than the control samples dyed with PDA directly at the same conditions.