Used in hair dye formulations as a coupler to develop stable, long-lasting color. It reacts with primary intermediates like p-phenylenediamine in oxidative dyes to form larger colored molecules that remain in the hair shaft. Its structure allows for a range of shades, particularly natural brown to black tones. Also helps improve color intensity and gray hair coverage. Commonly found in permanent and semi-permanent hair coloring products. Requires alkaline conditions to activate, often combined with hydrogen peroxide for oxidation.