Used primarily as a hair dye component, it functions as a coupler in oxidative hair coloring systems. It reacts with primary intermediates like p-phenylenediamine in the presence of hydrogen peroxide to form larger colored molecules that impart shade to hair. Provides natural-looking brown to black tones depending on the formulation. Also found in some semi-permanent and permanent hair color products due to its ability to penetrate the hair shaft and produce long-lasting color. Its amino and hydroxyl groups contribute to solubility and reactivity under alkaline conditions typical in hair dye mixtures.