Almost 50 per cent of women and a growing percentage of males are dissatisfied with their natural hair color. If you are considering a change of hair color it is worthwhile having some knowledge of how this may be achieved.
There are five basic types of hair color: gradual, temporary, semi-permanent, permanent, and bleaches.
Gradual hair colorants are most frequently promoted as a way of restoring color to grey or white hair. These dyes are composed of metallic salts that are rubbed onto the hair daily until shades of brown and black gradually appear. These preparations are not messy and are easy to use but have several disadvantages. They smell unpleasant, and because the metal salts are deposited on the outside of the hair cuticle they make the hair look dull and lifeless. In addition their presence precludes the use of permanent waves or coloring because the chemicals used in these other processes cannot penetrate the layer of metal salts coating the hair shaft. Finally these dyes cannot be removed from the hair shaft without causing hair damage and should be left to grow out.
Temporary hair coloring can be achieved with the use of synthetic compounds that are deposited on the outside of the hair shaft. These products are available as rinses, mousses, gels and sprays, and can be used to tone down brassy tones in bleached hair or to give a new but temporary party look— particularly when shades of green, blue and purple are used!
These dyes wash out with one shampoo. If the user is unfortunate enough to be caught in the rain the dye will run and stain both skin and clothing.
Semi-permanent hair dyes are the most popular form of hair dye and are used both at home and in hair-dressing salons. These dyes penetrate the cuticle (the outer layer of the hair shaft) to the hair cortex and will withstand 6 to 10 shampoos. They are most commonly used as a means of brightening or subduing natural or bleached hair color. They do not interfere with permanent waves or other hair processing. They are readily obtainable from chemists and supermarkets and are simple to use. These dyes rarely cause allergic contact dermatitis and can usually be tolerated by people who are allergic to permanent hair dyes.
Vegetable dyes are another form of semi-permanent hair color, and are derived from plants such as Roman or -German chamomile, logwood, walnut, and the North African shrub Lawsonia alba. Henna, which is used to give the hair rich red or auburn tones, is derived from the dried leaves of the latter. These dyes stain the cuticle and do not penetrate the hair shaft. They will not radically alter hair color but can be used to accentuate hair color and blend in grey hair. Like synthetic semipermanent dyes they have the advantage of washing out after a few shampoos and do not interfere with other hair processing.
Permanent hair coloring is so named because the dyes actually penetrate the hair shaft and form large color molecules that become trapped within the hair cortex. They cannot be removed by shampooing. Re-dyeing is necessary every 4 to 6 weeks to deal with the regrowth at the scalp. Permanent (or oxidative) hair coloring generates a complex chemical reaction within the hair shaft between the dye and a developer (also called an ‘oxidising’ agent). This results in the formation of a large color molecule. The developer is usually hydrogen peroxide, which has the additional effect of bleaching the natural hair color as the new color is being developed.
Permanent hair dyes are also known as para dyes or amino dyes because they contain paraphenylenediamine (PPD) or closely related chemicals. PPD can cause allergic contact dermatitis in up to 10 per cent of users. Furthermore, allergy may develop even after numerous trouble-free applications of these dyes. It is consequently recommended that the dye be applied to a small test site on the nape of the neck or forearm prior to applying these colorants. If the test site becomes itchy or red the para dyes should not be used.
Unfortunately the bleaching reaction which takes place within the hair shaft damages the keratin. As a result repetitive applications of permanent dyes can cause damage and breakage of the hair shaft. Dyeing should not be carried out more frequently than every 3 to 4 weeks and the dye should only be applied to the regrowth.