In hair coloring, what is the purpose of a developer?

In hair coloring, the purpose of a developer is to activate the color and assist in its penetration into the hair shaft. The developer contains hydrogen peroxide, which acts as an oxidizing agent. When mixed with hair color, it opens up the hair cuticle, allowing the color to enter and bond to the hair structure. This process is crucial for achieving the desired shade and ensuring that the color lasts.

The developer's role is vital because without it, the color molecules would not be able to penetrate effectively, leading to poor color results. This activation is especially important with permanent and some semi-permanent hair colors, where a chemical alteration of the hair structure is necessary to ensure the longevity of the color.