HAIR COLORING

HAIR COLOURING

Hair coloring is the practice of changing the color of hair. The main reasons for this practice are cosmetic (e.g., to cover gray hair, to change to a color regarded as more fashionable or desirable, or to restore the original hair color after it has been discolored by hairdressing processes or sun bleaching). Hair dyeing, which is an ancient art, involves treatment of the hair with various chemical compounds. Today, hair coloring is immensely popular, with over 75 percent of american women dyeing their hair.

TYPES HAIR COLOURING

The four most common classifications are permanent, demi-permanent (sometimes called deposit only), semi-permanent and temporary.

PERMANENT HAIR COLORING
A very popular way to achieve permanent hair coloring is through the use of oxidation dyes. The ingredients of these products include 1,4-diaminobenzene (historically) or 2,5-diaminotoluene (currently), a coupling agent, and an oxidant. The process is typically performed under basic conditions.

The mechanism of oxidation dyes involves three steps:

 1) Oxidation of 1,4-diaminobenzene derivative to the quinone state.

 2) Reaction of this diimine with a coupler .

 3) Oxidation of the resulting compound to give the final dye.

Various combinations of primary intermediates and couplers provide a spectrum of shades of hair colors. The primary intermediates are aromatic para compounds, such as 1,4-diaminobenzene or 4-aminophenol. The couplers are meta-substituted derivatives of aniline. They come in three major classes based on the color that they produce when they react with the primary intermediate.

• Blue couplers include 1,3-diaminobenzene and its derivatives.
• Red couplers include phenols and naphthols, such as 3-aminophenol, 5-amino-2-methylphenol  and 1-naphthol. The combination of 2,5-diaminotoluene with the coupler 3-aminophenol gives a magenta-brown dye, while the combination of 2,5-diaminotoluene with the coupler 1-naphthol gives a purple dye.
• Yellow-green couplers include resorcinol, 4-chlororesorcinol, and benzodioxoles. These compounds produce broad-band absorption when they react to form dyes, allowing for more natural-looking hair colors. The combination of 2,5-diaminotoluene with the coupler resorcinol gives a greenish brown dye.

The first step shows the oxidation of p-phenylenediamine to the quinonediimine (C₆H₄(NH)₂)

This species exists in equilibrium with the monoprotonated form (C₆H₄(NH)(NH₂)⁺) (not shown). The second step involves the attack of this quinonediimine on the coupler. In organic chemistry, this reaction is called electrophilic aromatic substitution

In the third and final step, the product from the quinonediimine-coupler reaction oxidizes to the final hair dye.

The resulting hair dye is also much larger than the precursor molecules, which causes the dye to bond to the hair

DEMI-PERMANENT HAIR COLOR

Demi-permanent hair color is permanent hair color that contains an alkaline agent other than ammonia (e.g. ethanolamine,sodium carbonate) and, while always employed with a developer, the concentration of hydrogen peroxide in that developer may be lower than used with a permanent hair color. Since the alkaline agents employed in demi-permanent colors are less effective in removing the natural pigment of hair than ammonia these products provide no lightening of hair's color during dyeing

Demi-permanents have several advantages as compared with permanent color. Because there is essentially no lifting (i.e., removal) of natural hair color, the final color is less uniform/homogeneous than a permanent and therefore more natural looking; they are gentler on hair and therefore safer

SEMI-PERMANENT HAIR COLOR

Semi-permanent hair color has smaller molecules than temporary dyes. These dyes only partially penetrate the hair shaft. For this reason, the color will survive repeated washing, typically 4–5 shampoos or a few weeks. Semi-permanents contain no, or very low levels of developer, peroxide or ammonia, and are therefore safer for damaged or fragile hair. However, semi-permanents may still contain the possibly carcinogenic compound p-phenylenediamine or other such ingredients.

TEMPORARY HAIR COLOR

Temporary hair color is available in various forms including rinses, shampoos, gels, sprays, and foams. Temporary hair color is typically brighter and more vibrant than semi-permanent and permanent hair color.Temporary hair color is available in various forms including rinses, shampoos, gels, sprays, and foams. Temporary hair color is typically brighter and more vibrant than semi-permanent and permanent hair color.

ADVERSE EFFECT OF HAIR COLORING

1. HAIR BREAKAGE .Hair that has been damaged by excessive exposure to chemicals is considered over-processed. The results in dry, rough and fragile hair. In extreme cases, the hair can be so damaged that it breaks off  entirely. This is especially true for Afro-Caribbean hair, especially if used in combination with relaxers. Treatments are available but the only real solution is to stop the use of chemicals until new hair grows and the damaged hair is cut off. 
2.  SKIN IRRITATION AND ALLERGY. In certain individuals, the use of hair coloring can result in allergic        reactions and/or skin irritation.Symptoms of these reactions can include redness, sores, itching, burning sensation and discomfort. Symptoms will sometimes not be apparent immediately following the application and processing of the tint, but can also arise after hours or even a day later. To help prevent or limit allergic reactions, the majority of hair color products recommend that the client conduct a patch test before using the product. This involves mixing a small quantity of tint preparation and applying it directly to the skin for a period of 48 hours. If irritation develops, manufacturers recommend that the client not use the product.