Before a new color can be deposited onto the hair, the natural pigment first needs to be oxidized with hydrogen peroxide. This enables the new color to be better "grabbed" by the hair, making it both more intense and longer lasting.
In oxidizing creams and hair dye developers, hydrogen peroxide opens the cuticle layer through its oxidizing effect and penetrates the structure of the hair.
Persulfates are also strong oxidizing agents that are used in the cosmetics industry as hair bleach boosters.