Permanent Hair Dye
To understand how permanent hair dye works, one needs to understand some basic physiology about hair. If you look at the hair on anyone's head, what you see is the shaft. The roots push each piece of hair fiber (or hair follicle) through the scalp, at which point the hair we see (the shaft) is in fact biologically dead. Only the hair in the root itself is alive. Yet each single hair has the most amazing structure and very definite characteristics that affect the appearance of the hair and how it performs in terms of porosity, elasticity and texture.
The texture of our hair is affected by the general thickness of the shafts and the way the cuticle around each shaft adheres to the inner cortex. Soft hair is generally easier to color than hair that has a very coarse texture. Another factor is the porosity of the hair shaft, which relates directly to the amount of moisture it absorbs. Nice healthy hair shafts are naturally impermeable to moisture. But when we color and perm our hair (to make it curly or wavy), or straighten it, we very often damage the cuticle, making it less permeable, which can easily lead to damage of the cortex. What you would notice is that your hair becomes dry and the ends start splitting. Damage to the cortex will also affect the elasticity of the hair shaft, which leads to further breaking.
Hair shafts are made up of various proteins, primarily fibrous keratin, which is also found in our skin and fingernails. Melanin, a type of pigment that colors both our skin and our hair, is also found in different forms:
- eumelanin produces black and brown colors;
- phaemelanin produces different shades of blond, red and ginger;
- a lack of melanin (usually as we get older and the body stops producing these colored pigments) results in hair that is grey or white.
When we color our hair using permanent hair dye products, chemicals (primarily ammonia) are used to open up the cuticle and cortex of the shaft. The colorants are then able to bind permanently to the keratin.
There are different kinds of permanent hair dyes including those that are considered to be "progressive" and others that rely on oxidation. Both of these require the cuticle to be opened so that the dye can penetrate the hair shaft and color the hair molecules. The type that relies on oxidation uses phenylenediamines (originally patented by German scientist E. Erdmann in 1888).
"Progressive" hair dyes contain lead acetate and are therefore a trifle controversial since lead is poisonous. In 2002 the United States Food and Drug Administration (the FDA) undertook stringent trials with people using products containing lead acetate and found that lead was not absorbed into the blood stream, specifically when the products are used progressively. Small quantities of this ingredient are legally allowed to be used in hair dye. However they also insist that if it is used, this should be listed on the packaging with a caution that it should only be used externally, and only on the scalp – definitely not on your eyebrows or to color your pubic hairs.
When permanently dyeing hair, progressive dyes are favored by many people as they change your hair color more gradually, and the color builds up, getting darker over time.
When we use a lighter shade than our natural hair color, bleach incorporated in the product will lighten the hair, and the colorant will color it. Essentially then there are two processes taking place simultaneously: the bleach alters the original hair color and lightens it, and the colorants dye the hair a new color, or add color to your graying roots.
Since your original hair color will always impact on the final result (unless you bleach your hair white prior to coloring) most products show the probable or approximate color results expected from the permanent hair dye on the packaging.