Which type of dye typically requires a developer to activate its colour process?

Permanent dye requires a developer, often referred to as an activator, to activate its color process. This is because permanent hair color contains ammonia or an alkaline agent that opens the hair cuticle, allowing the dye to penetrate the hair shaft. The developer, usually hydrogen peroxide, provides the necessary oxidative process that develops the color and ensures it lasts longer by actually altering the natural pigment of the hair. This makes the color change permanent until the hair grows out or is cut.

In contrast, semi-permanent dye does not usually require a developer, as it is designed to coat the hair rather than penetrate deeply. Temporary dyes, on the other hand, only last until the next wash and do not need a developer because they are not meant to penetrate the hair cuticle. Direct dyes are a form of semi-permanent color that can be applied directly to the hair without any activation needed through a developer. Therefore, the need for a developer is a key distinguishing factor for permanent dye.