Black, Brown, Red, or Yellow!


What on Earth would we do if hair dye was taken away from us? It is a wondrous substance that helps cover grey hair and keep us looking young. It gives us that extra boost in our appearance, which goes hand in hand with developing our personalities and the way we interact with others.

Hair coloring is very popular today, with over 75% of women coloring their hair and a growing percentage of men following suit. How does hair color work? It is the result of a series of chemical reactions between hair molecules, pigments, as well as peroxide and ammonia, if present.

What’s in a Hair?

Hair is mainly keratin, the same protein found in skin and fingernails. The natural color of hair depends on the ratio and quantities of two other proteins, eumelanin, responsible for brown to black hair shades, and phaeomelanin; responsible for golden blond, ginger and red colors. The absence of either type of melanin produces white/gray hair.

Bleach is used to lighten hair. It oxidizes melanin molecules in hair, removing the color in an irreversible chemical reaction; the melanin remains present, but the oxidized molecules become colorless. However, bleached hair tends to have a pale yellow tint; yellow is the natural color of keratin. Moreover, bleach reacts more readily with the dark eumelanin pigment than with phaeomelanin, so some gold or red residual color may remain after lightening.

Color Me This!

Up until the 19th century, the only dyes available were those prepared from natural sources; by combining various plant extracts, it was possible to create a fairly extensive range of colors. Indigo, for example, could be mixed with henna to give varying shades of brown.

Other substances that have been used for dyeing hair or wigs are rock alum, black sulfur, honey, in addition to lead, quicklime, salt, or silver nitrate in rose water. Another early method of coloring hair was to apply powders made of wheat starch, powder of potato starch combined with chalk, burnt alabaster, colorants, burnt sienna or umber.

Many different plant extracts were used for hair dye in Europe and Asia before the advent of modern dyes. An extract of the flowers of the chamomile plant was long used to lighten hair, and it is still used in many modern hair preparations. Other dyes were produced from walnut leaves or nut husks, and from the galls, a species of oak trees. Some of these plant-derived dyes were mixed with metals, such as copper and iron, to produce more lasting or richer shades.

Hair Coloring Made Possible

The outer layer of the hair shaft, its cuticle, must be opened before permanent color can be deposited into the hair. Once the cuticle is open, the dye reacts with the inner portion of the hair, the cortex, to deposit or remove the color. Most permanent hair colors use a two-step process, usually occurring simultaneously; first removing the original color of the hair, then depositing a new color.

Ammonia is the alkaline chemical that opens the cuticle and allows the hair color to penetrate the cortex. It also acts as a catalyst when the permanent hair color comes together with the peroxide, which is used as the developer or oxidizing agent that removes pre-existing color.

Peroxide breaks chemical bonds in the hair, releasing sulfur, which accounts for the characteristic odor of hair color. As the melanin is decolorized, a new permanent color is bonded to the hair cortex. Various types of alcohols and conditioners may also be present in hair color. The conditioners close the cuticle after coloring to seal in and protect the new color.

The Dye Revolution

The late 19th century saw the introduction of hydrogen peroxide as an efficient hair lightener; thus, ushering in the experimentation of chemical compounds to produce a synthetic dye. The first chemical compound developed was pyrogallol, used since 1845, in combination with henna, to dye hair brown.

The 1880s saw the introduction of amino dyes of which p-phenylenediamine was the earliest. Before being applied to the hair, it is mixed with caustic soda, sodium carbonate, or ammonia. Hydrogen peroxide was then applied, which then brought out the color.

In 1950, Clairol was the pioneer of the one-step hair dye, which made the process of hair dyeing much easier; the time-consuming shampoo and pre-lightening steps could be eliminated.

But what do modern hair dyes contain? They generally contain dyes, modifiers, antioxidants, alkalizers, soaps, ammonia, wetting agents, a plethora of different fragrance, and a mixture of other compounds used to impart different qualities to hair depending on hair type, color and texture. Metal oxides, can also be added as pigment.

Resorcinol is a commonly used modifier, used to bring out the tone of color or set the dye. The dye is prevented from oxidizing with air by means of an antioxidant such as sodium sulfite. Dyes work most efficiently in an alkaline composition so alkalizers, such as ammonium hydroxide, are added.

Added to these basic chemicals, will be a variety of chemicals to give a certain dye solution certain qualities suitable for different hair types. There are various types of hair dyes on the market, such as temporary hair colors and semi permanent dyes, which penetrate into the hair shaft but wash out of the hair after 5-10 shampoos.

The next time you reach for that bottle of dye or sit patiently in the hairdressing salon, as the smells of the chemicals waft around your nose, you can reflect on the long journey of those dyes and what a boring world it would be without them.


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SCIplanet is a bilingual edutainment science magazine published by the Bibliotheca Alexandrina Planetarium Science Center and developed by the Cultural Outreach Publications Unit ...
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