Sunlight-induced Permanent Hair Dyeing

Hair coloring has emerged as an integral part of the cosmetic industry, particularly in response to the increasing global aging phenomenon. The natural melanin analog, polydopamine (PDA), has garnered considerable attention as an eco-friendly hair dye, and several kinds of polymerization ways of dopamine (DA) have been proposed including alkali catalysis, metal ion catalysis, strong oxidants, and enzyme-mediated oxidation reactions and polymerizations. Yet the controllability of polymerization and potential toxicity of involved metal ions are still in question. Inspired by the photoprotective mechanism in human skin, we have developed the melanin-inspired hair dyeing strategy that allowed for the in situ oxidative polymerization of DA under ultraviolet (UV) light. This polymerization was triggered by photobase generators (PBGs), a class of compounds that produced organic bases upon UV and sunlight irradiation. The resulting hair showed an adjustable color from light brown to black by tuning the ratio of DA and PBG (DA@PBG), the concentration of DA, and light exposure time. The dyed hairs showed excellent washing resistance and superior anti-static properties. Furthermore, Hair Color Spray DA@PBG also demonstrated a desirable hair dyeing effect and excellent biosecurity by simply spraying it on the hair under sunlight. This novel sunlight-induced method provided a new direction towards the preparation of natural hair dyes and could promote the development of green and safe hair dyes in colorful and brilliant artistic-grade hair coloring.