Acid dyes are a type of synthetic dye that are soluble in water and are primarily used to color proteins and polyamide fibers, such as wool and silk. They are called "acid" dyes because they are applied in an acidic dye bath, which helps the dye molecules bond to the fibers. These dyes are known for their bright colors and excellent colorfastness. These dyes work by forming ionic bonds with the fibers, making them suitable for a variety of applications, including textiles and leather. Acid dyes can also be used in the food industry and for coloring cosmetics, showcasing their versatility beyond just fabric dyeing.