Haircoloring products generally fall into four categories: temporary, semi-permanent, demi-permanent and permanent. Today I will explain the chemical action of permanent haircolor, which, along with demi-permanent formulas, is most widely used in salons.
Permanent haircolor is most often used when 1) covering grey hair and/or 2) a shade lighter than the natural shade is desired. They typically contain an alkalizing ingredient (usually ammonia), and oxidizing ingredient (usually peroxide), and tints.
The oxidizing ingredient creates oxygen, which is essential to both lightening and developing color molecules. Lightening occurs when an alkalizing agent is added to peroxide or oxidizing agent. The peroxide becomes alkaline and is able to penetrate the cortex and break up the melanin located in the cuticle. The higher the volume, or concentration, of peroxide, the more lightening you will experience.
Permanent tints begin very small, in fact they are initially dye precursors. Once they enter the cuticle, they expand with the aid of hydrogen peroxide into larger tint molecules. These molecules are then trapped in the hair shaft and can not be shampooed out. This is what makes permanent haircolor permanent.
To recap, permanent haircolor opens the outer layer of your hair strand to allow small dye particles to enter the inner layer. Once inside, the tints oxidize to create larger molecules that remain in the hair’s core. They can simutaneously lift natural haircolor and deposit artificial haircolor, making it a snap to go a bit lighter or cover grey.