Hair coloring products
Natural hair color is derived from melanin granules embedded throughout the cortex of hair fibers. Two general classes of such pigments have been identified: eumelanins and pheomelanins. The combination ratio and concentration of these two types of pigments impart to the hair its characteristic natural gradations of color. Dark hair has a higher concentration of the eumelanins, while red hair has a predominance of the pheomelanins. Light blond hair has reduced amounts of both. Hair bleaching is a chemical process by which the melanin pigment granules are gradually destroyed by the bleaching agent, resulting in lighter hair color. Hair coloring is undertaken to change or cover the color of hair for many different reasons. For instance, hair is often colored to cover hair that has turned gray, to lighten or change the shade of hair, or to highlight or lowlight hair. The hair coloring procedures used to generate these results are often markedly different and use different coloring materials. Coloration of hair is a procedure practiced from antiquity employing a variety of means. In modern times, the most extensively used method employed to color hair is to color hair by an oxidative dyeing process employing hair coloring systems utilizing one or more oxidative hair coloring agents in combination with one or more oxidizing agents. Hair coloring compositions contain various types of coloring agents, specifically, permanent, semi-permanent or direct, and temporary colorants. The permanent hair dyes generally refers to oxidative hair color that bleaches the melanin found in the hair shaft as well as imparting color. The activated peroxide in the oxidative dye composition provides a bleaching effect while the oxidative dye molecules penetrate the hair shaft and polymerize therein. While hair that is oxidatively colored provides a certain permanence, re-coloring every four to six weeks may be necessary due to new hair growth. Permanent hair dyeing formulations typically comprise oxidative hair dye precursors, which can diffuse into the hair through the cuticle and into the cortex where they can then react with each other and suitable oxidising agents to form the end dye molecules. The semi-permanent or direct hair dyes are preformed dye molecules that are applied to the hair and provide color for about six to twelve shampoos. This type of hair dye is gentler to the hair because it does not contain peroxides, but the hair color does not last as long. Temporary hair dyes are dye molecules or pigments that are too large to diffuse into the hair shaft, and therefore act on the exterior of the hair. Consequently, temporary hair dyes are generally removed after one or two shampoos. Semi-permanent hair color generally provides more lasting color than temporary dyes but without the permanence and commitment of oxidative color. Semi-permanent color is a single component product. Many of such products contain two types of dyes: one of smaller molecular size (such as nitrophenylene diamines and nitroaminophenols) that are capable of penetrating the hair shaft and being retained within. The second type of dye used in semi-permanent hair color has a larger molecular size and is too large to penetrate the hair shaft of normal virgin hair. Temporary hair color is often found in the rinse form, and typically lasts for one shampoo. Such hair color is often used when special effects is desired. Temporary color simply coats the hair shaft with colorants that are too large to penetrate its outer surface. Minor penetration of the hair shaft may occur in individuals with damaged or porous hair, but such color application rarely lasts through more than one or two shampoos.
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