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Whether it's nice and easy, or just because you're worth it, hair dyes have been raising in popularity. More people are dying their hair now: men, women, young, and old - People no longer ask, "Who cut your hair?", but now ask, "Who does your colour?"

The idea of permanent hair dye is not new. The ancient Egyptians used henna to colour their hair red or orange, and the Romans used the extract from boiled walnuts and leeks to dye their hair black.

In this day and age, however, hair dye has moved away from the use of plants to the use of chemicals. It is really just Chemistry. The first commercial hair dye was developed by a French chemist, Eugene Schueller, who went on to create the company L'Oreal. While what can be purchased today is more advanced then his original invention, the chemistry has remained nearly the same.

To get how hair dye works, hair itself needs to be understood. Hair consists of a shaft, which sticks out of the skin, and the root, which is attached beneath the skin's surface in a follicle. Except for a few cells where it grows out of the skin, hair is just dead tissue. The shaft is made mainly of keratin and consisting of three parts: The outer layer of the hair shaft is called the cuticle and is made up of transparent cells which overlap each other like scales on a fish; the middle layer is the cortex, where the pigmentation occurs; and the core of the shaft is the medulla.

Did you know? The primary component of hair is the protein keratin.

A stand of hair has 3 layers: the cuticle, the cortex and the medulla. Pigments that give hair its colour are found in the cortex. The colour of hair comes from proteins called melanins. There are two kinds of melanins - eumelanin which makes hair brown to black and pheomelanin which is responsible for blond, red, and ginger coloured hair. A loss of pigmentation, (i.e., a decrease in these melanins) is what causes hair to gray or turn white.

Now, to change the natural colour of your hair, there are two choices: temporary, meaning if you change your mind it will wash out after a few shampoos, and permanent.

For significant colour changes (i.e., for the brunette to really wants to see if blonds have more fun) permanent colouring is needed. Permanent colour involved two steps: it first removes the hair's natural pigments, and then chemically adds the new shade.

The first step is to destroy the melanin by breaking up some of the chemical bonds. To gain access to the melanin, however, the overlapping "scales" of the cuticle need to be opened. Ammonia (NH3) is used for this process because it swells the hair, creating openings in the cuticle for the dye and hydrogen peroxide to get through. Also, ammonia acts as a catalyst in the second step when the actual dying takes place.

Once the cuticle has been opened up, hydrogen peroxide (H2O2) goes into action and to disrupt the melanins. Hydrogen peroxide (H2O2) is a strong oxidizing agent that is used to oxidize the melanin molecule and remove hair's natural pigment.

But, H2O2 also has a job in the second step, when the permanent colour is added to the hair. When the dye is added to the hair it is added as two distinct chemicals: phenylenediamine known as the "primary" and aminophenol known as the "coupler". A chemical reaction between these two compounds produces a coloured product that is responsible for dying the hair. However, the primary and the coupler do not react with each other until they have mixed with the H2O2.

Once the two chemicals are combined inside the cortex in the presence of H2O2, the reaction occurs; the primary and coupler bind together forming a coloured molecule that is too big to escape the "scales" of the cuticle. So, the newly formed coloured molecules are now permanently stuck in the hair and will not be removed with shampooing.

This means that when you dye your hair you have to be pretty confident with your colour choice since you will be looking at it until grows out, or until you dye it again. Maybe next time you can try "cherry bomb", "electric blue", or "iguana green"! But if you are planning a colour change, keep in mind that damage to the hair will eventually occur with excessive colouring.


Corbett, J.F. (1991). Hair coloring processes. Cosmetics and Toiletries, 106 (7): 53 — 58.

Schwarcz, J. (2004) 'Do or dye? Do blondes have more fun? At what cost? Before you head back to the beauty salon, read up on chemistry and complexities of colouring your hair. Canadian Chemical News, 56 (7): 29 - 31

Learn More!

How Stuff Works:

Exploratorium Online "Better Hair Through Chemistry":

Style Hair Magazine Online:

Angela Hill BSc, BJ, is a journalist and photographer currently working at a daily newspaper. She has no patience with food photography and was a little scared by the thought of an exploding hot dog. She spends her time photographing people and hopefully exotic places.


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