Permanent dye is a type of hair color that provides long-lasting results. It penetrates the hair shaft, allowing the color to remain vibrant even after multiple washes. This dye is often used to cover gray hair or to achieve a dramatic change in hair color. Unlike temporary or semi-permanent dyes, which wash out over time, permanent dye requires a chemical process that typically includes ammonia and developer. This process opens the hair cuticle, enabling the dye to bond with the hair. As a result, permanent dye can last for several weeks or even months, depending on hair care practices.