Hair colouring has been practised by both men and women since the days of the Pharaohs. Primarily it is used Co conceal the onset of greying, but with the development of more sophisticated and simpler techniques the changing of hair colour has become a pursuit of fashion. Originally vegetable dyes such as henna and camomile were mainly used. These were certainly safer than, if not quite as effective as, the newer products. Metallic dyes, sometimes known as ‘colour restorers’, are mainly used by men to gradually dye grey hair. These dyes are usually made from the salts of lead (resulting in a black colour) or bismuth (resulting in a brown colour). With frequent applications, they gradually change the hair colour. They are relatively easy and safe to use.

The hair dyes most commonly used by women today are the synthetic organic dyes. There are three main types available. The temporary ones simply coat the hair shaft with pigment, without penetrating it. They are usually applied as a rinse, and may be removed by shampooing. Semi-permanent dyes are the most popular. These penetrate the hair shaft, without drastic pre-treatment, and persist tot six to ten shampoos. They are mainly nitro or azo dyes. The permanent, or oxidative, dyes are mainly para-phenylenediamine mixed with hydrogen peroxide. Their main disadvantage is that a significant proportion of people are allergic to them, and there is some as yet unconfirmed evidence that they may produce cancer in some experimental animals.

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