Abstract: Continued contact of some chemicals with the skin is known to cause contact dermatitis and even in exceptional cases contact leucoderma. In our earlier study some of these chemicals specially azo dyes have been found to interact with human (Calf thymus) DNA, probably causing the inactivation of melanocytes. In an effort to find out the mechanism of interaction of some commercial dyes on human skin, the in vitro studies have been reported on the CT-DNA-azo dyes interaction. In the present article the process of melanogenesis, properties and functions of melanin, the enzymes involved in its synthesis as well as chemically induced leucoderma have been reviewed.