Review:Mechanism of Hair Dying and Their Safety Aspects

An original hair color change by application of chemical dye is a common practice among the men and women. Hair dyes are classified into the following category based on their color retention property, namely temporary, semi permanent, demi permanent and permanent. Temporary dyes are otherwise called as non-oxidative dyes;because coloring process was carried out without any oxidizing agent, it reduced stay time on the fiber, removing the hair during the first shampoo wash. Semi permanent products consist of nitro aromatic amines or aromatic amino nitroanthroquinone dyes, which diffuse into the hair and bind to the hair;however do not attach firmly. Permanent hair dyes are called oxidation hair dyes;because of the oxidizing agent used for the color development. An active intermediate reacts further with coupler and provides the color to the hair and in general oxidation hair dyes provides shampoo resistant hair dyes. Some hair dyes can cause allergic reactions or sensitization that may result in skin irritation and hair loss. People can develop sensitivities with repeated exposure. Also, formulations may change over time. The primary toxicological concerns of hair dyes, primarily oxidation hair dyes, are with contact dermatitis and long-term "potential" systemic effects. The para diamine oxidation derivative dyes reported to having more sensitizing potential when compared to other amine derivatives. P-Phenylenediamine is the major component of oxidation hair dyes, and oxidation dyes are the most widely used of all hair dyes. Therefore PPD is the sensitizer of prime concern.