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March 13,2000
Volume 78, Number 11
CENEAR 78 11 p.52
ISSN 0009-2347

Hair Coloring

Hair Coloring
[Photo by Cliff Braverman]
Ever since Madonna became a star in the mid-1980s, I—a natural brunette—had a not-so-secret desire to be a blonde. Over the years, I made and canceled a few appointments to have my hair colored. I just never had the nerve to go through with it until last summer, when my gray streak had gotten so big it was no longer a fashion statement, it was—well—gray hair!

So, I kept that last appointment. I was really going to take the peroxide plunge. Sitting in the salon, my hairdresser took what looked like a pastry brush and saturated my hair with clear whitish goo that looked like icing for cinnamon buns and told me, "There's no turning back, now." When I asked, "What's that stuff?" he said he didn't know. "You have the chemistry degree," he reminded me. A little while later, with ammonia and other smells in the air, I didn't need a degree to tell me that there was some serious chemistry going on up there.

Curious, I began looking around and found out that there is some pretty interesting chemistry involved in coloring hair. Here is what I learned: People have been changing the color of their hair for millennia, but it wasn't until 1907 that French chemist Eugène Schueller created the first safe commercial hair coloring. His invention was based on p-phenylenediamine that later provided the foundation of his company, the French Harmless Hair Dye Co., which became L'Oréal .

There are several basic types of hair dyes on the market. There are temporary hair colors, which are applied in the form of rinses, gels, mousses, and sprays. They coat the surface of the hair and usually wash out within two or three shampoos. Semipermanent dyes penetrate into the hair shaft, but not as deeply as permanent dyes. Although semipermanent dyes do not rinse off with water, they do fade and wash out of hair after about five to 10 shampoos.

Gradual or progressive dyes—like Grecian Formula 16—surprised me. They are usually marketed to men and contain lead acetate [Pb(CH3COO)2]. As the solution is rubbed on the hair, it penetrates the cuticle and the Pb2+ ions react with sulfur atoms in the proteins to form lead sulfide (PbS), which is a dark color. The more frequently the solution is applied, the darker the, ahem, lead head.

The most interesting chemistry to me, however, was the chemistry of permanent hair dyes—especially those that lighten and color in one process. These formulations penetrate deeply into the hair shaft and don't wash out.

Before any permanent color can penetrate the hair shaft, the cuticle, or outer layer, must be opened so that chemicals can get in to the natural pigment molecules. Under a microscope, the cuticle of human hair looks a lot like overlapping snake scales. The pigments, which are protein granules, are stored in the cortex of the hair beneath the scaly cuticle layer.

There are two types of melanin protein found in the hair: eumelanin, which is responsible for hair shades from black to brown, and phaeomelanin, which is responsible for red and yellow-ish colors. Absence of pigment, which was my problem, produces white or gray hair. The melanin type and granule size determine the color of hair, while the density of distribution of these pigment granules determines how light or dark the hair is. But enough on natural hair color.

Permanent hair-coloring products consist of two components that are packaged separately and mixed together immediately before application. One package contains a solution of hydrogen peroxide (usually 6%) in water or a lotion base. The other package usually contains an ammonia solution of dye intermediates and preformed dyes—called couplers. The primary intermediates are ortho or para diaminobenzenes, aminohydroxybenzenes, and to a lesser extent dihydroxybenzenes that develop color on oxidation. The color couplers don't oxidize readily but react with the oxidized primary intermediates to provide a wider variety of colors. The couplers are phenols, meta disubstituted phenylenediamines and phenyleneaminophenols, and various resorcinol (1,3-dihydroxybenzene) derivatives.

As soon as the ammonia dye solution and the hydrogen peroxide solution are mixed together, they are applied to the hair. The ammonia in the mixture (less than 1% concentration) causes the hair to swell and the cuticle scales to separate a little. After this happens, the dye precursors are able to penetrate the cuticle before they have fully reacted with each other and with the hydrogen peroxide. This is why even when brown hair coloring is first applied it looks whitish. This is also why you have to wait a half hour or more for the color to develop.

Darker shades are obtained by using higher concentrations of intermediates. Tones can also be adjusted. For example, addition of resorcinol will make a shade more yellow, while adding 4-amino-2-hydroxytoluene will make the shade redder. Sometimes dyes are used along with the oxidation dye intermediates to add vibrancy to the tone that is not otherwise available. Usually these dyes are used to add intensity to gold or red shades.

I never had a desire to look like Lucille Ball, so I don't think I'm going to go for red hair, but if I did, the formulation used most likely would contain 2-nitro-p-phenylenediamine. I understand that this orange-red color would be quite bright and that the narrower absorption spectrum of this dye produces much purer hair color than the broader visible absorption bands of other dyes. Sounds intense.

I'm glad I have all these choices and don't have to be gray-haired before I want to be. Let's hear it for better—and blonder—living through chemistry!

Linda Raber

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