Brilliant Blue FCF or Acid Blue 9 (CI 42090) is a synthetic organic, water-soluble colorant belonging to the triphenylmethane dye family. Widely recognized for its intense, vivid blue hue, it is used across the food, pharmaceutical, and cosmetic industries. In the European Union, it is approved as a food colorant under the designation E133, and it is also authorized for use in cosmetic products, including those applied to the lips, face, and eye area. It functions as a direct dye, providing strong color even at low concentrations. It is commonly found in personal care items like soaps, bath bombs, or toothpaste. Depending on the formulation, it may be used alone or blended with white pigments such as titanium dioxide to create lighter blue shades. This colorant is appreciated for its excellent stability, resistance to light and pH variations, and its ability to disperse evenly without forming aggregates. Its concentration in the finished cosmetic product should not exceed 0.5% of pure Brilliant Blue FCF, ensuring safe use while maintaining effective coloration in line with regulatory guidelines.