The Mechanics of Changing your Hair Color
Changing the color of hair is a chemical process. The simplest change is to remove all color with a bleaching agent-most commonly, hydrogen peroxide-leaving the hair a featureless white or yellowish white. All other changes of hair color are complex reactions of chemicals in the hair-coloring product with chemicals and biochemical in hair.
Coloring Agents
Four types of hair coloring agents are available for use by the consumer:
1. Gradual - an aqueous solution of a metal salt such as lead acetate. The colored hair may be rendered dry and brittle.
2. Temporary - color is added after one shampoo and removed with the next. The coloring agents are actually dyes adapted from the textile industry.
3. Semi-permanent - polymers or vegetable dyes that will stay in the hair through multiple shampoos.
4. Permanent - color chemically alters and binds to the hair cortex proteins (keratins); this alteration of keratins decreases the strength of their chemical bonds and this decreases the strength of the hair shaft. Permanent coloring agents do not require re-dyeing until the colored hair grows out and shows roots. While these are the most popular of all hair-coloring agents, they are also the most damaging of all coloring methods.
Frequent use of hair coloring increases the probability for permanent hair damage.
The chemicals in the hair-coloring product have specific functions to insure the correct color alteration. They need to:
1. Prepare hair to accept the hair dye
2. Alter the hair-shaft biology to maximize color change
3. Minimize chemical damage to the hair shaft
4. Set the dye to make the color change permanent until the dyed hair is shed in the normal cycling of hair growth.
Chemicals commonly listed on hair-coloring kits include:
| Chemical | Function |
| Hydrogen peroxide | Bleaching |
| Ammonia, monoethanolamine | Bleaching; making hair fibers swell for better acceptance of dye |
| Disodium phosphate, citric acid | Buffering agent; stabilizing chemical reactions |
| Sodium lauryl sulfate, cocoamide MEA, Oleth-5 | Foaming, thickening |
| Glyceryl stearate | Emmolluent |
| P-aminophenol, 1-naphthol, P-phenyl-enediamine,4-amino-2-hydroxytoluene | Dye vehicle |
| Propylene glycol, ethanol, glycerin | Dye precursors |
| Polyquaternium | Conditioner |
Adapted from pgbeautyscience.com
The list is not exhaustive; many other chemicals may be in the formulation of a hair coloring product, depending on the color change to be achieved (see http://www.pgbeautyscience.com).
Physical Changes to Colored Treated Hair
The hair shaft is a biologic fiber consisting of layers of structured proteins (keratins) and protectives oils (see Hair as a Biologic Fiber). In order for hair color to be changed, the oils have to be partially removed and the keratins that make up the structure of the cortex and the outer protective armor have to be "softened" in order for them to accept the hair dye. The natural oils of the hair shaft are altered or removed by a bleaching agent. These changes in the structural keratins and protective oils make the hair shaft "dryer" and more brittle than it is naturally. While a single hair-color change may not result in irreversible damage, more frequent hair-color changes (e.g., weekly to monthly) may result in irreversible damage such as split ends and dry, hard-to-comb "weathering".
Minimizing Damage from Hair Color Change
Hair damage beyond the damage necessary for effective hair coloring can be caused by:
- Hail color change more often than once every 4 to 6 weeks;
- Harsh shampoos; damage to dyed hair can be minimized by using conditioning shampoos (see Healthy Hair), or using silicone-containing conditioners after shampooing;
- Water exposure by swimming or frequently washing hair in plain tap water; the protective layers in hair that have been damaged in the process of hair coloring do not protect hair from being "dried out" by excessive exposure to water; and,
- Excessive exposure to ultraviolet light (sunlight) can cause further weathering and cause hair color to fade.
Health Problems Caused By Hair Coloring
Allergic reactions to hair dyes are rare, but they do occur in some people. Hair-coloring kits usually recommend testing the product on forearm skin before applying it to the scalp. Products for coloring scalp hair should never be used on eyebrows, eyelashes or beards. Questions have been raised regarding the carcinogenic (cancer-causing) potential of hair dyes. Analysis of a large number of studies concluded that there is no evidence of increased risk for cancer associated with use of hair dyes.