How Permanent Hair Dyes Work

If you are thinking about coloring your hair, you might be interested to learn how hair dye works. Hair dye does two things at once: removing the hair’s natural color, and adding a new color with dye. Most permanent hair dyes have three active ingredients: peroxide, ammonia, and colorant.

Ammonia

Ammonia is used in hair dyes to allow the dye to penetrate the hair. The outer layer of your hair, the cuticle, is made of many tiny scales, and the ammonia separates the scales to expose the hair’s soft core. Once the cuticle opens up, the other chemicals can start to work.

Peroxide

Hydrogen peroxide is the main ingredient in hair bleach and also bleaching agent in hair dye. It strips the hair’s natural color, activates the colorant, and helps it bond to the hair shaft. Peroxide works by oxidizing the melanin in hair, turning it into a new, colorless molecule. It works faster on eumelanin, the pigment that creates brown and black hair, than it does on red-gold phaeomelanin, so depending on your hair texture and color, it affects your hair differently. Hydrogen peroxide can also bleach less permanent hair dyes, which is why re-dyeing your hair can have such unpredictable results.

Colorant

The formulas for different colorants vary widely, so it’s difficult to generalize about them. Most modern hair dyes now include multiple color ingredients that react to form larger dye molecules once they bond to the hair shaft, so they are longer lasting and harder for competitors to duplicate.  The colorant enters the core of the hair shaft and bonds to it so it stays there for weeks or longer.

The exciting thing about artificial colorants is that they are not limited by the spectrum of colors produced by the two melanins, so you can dye your hair almost any color you can imagine.

Finishing Touches

Once all these things have happened, your dye is done working, but many dyes also include some ingredients to re-close the cuticle of the hair shaft and soothe the scalp as they work. Since this process uses intense chemicals and actually changes the composition of the hair shaft, it’s very stressful on your hair and weakens it significantly. It’s a good idea to be ready to take very good care of your hair after it’s dyed, if you want to avoid breakage, split ends, and other unpleasantness.

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