Abstract: One of the remarkable abilities of the human eye is to recognize colors; therefore compounds like dyes are used to enhance the attractiveness of objects. Today, there are thousands of various types of dyes used widely in foods, pharmaceuticals, cosmetics, textiles and plastics, some of which may pose a risk to human and ecological health due to their toxic properties. Azo dyes are a group of compounds containing one or more R1-N=N-R2 bonds. Studies have shown that both mammalian and microbial azoreductases cleave the azo bonds of the dyes to form compounds that are potentially genotoxic. The human gastrointestinal tract and skin harbors a diverse microbiota comprised of thousand species. Both water-soluble and water-insoluble azo dyes can be reduced by commensal bacteria. Some of the metabolites produced by the bacteria have been shown to be carcinogenic to humans although the parent azo dyes may not be classified as being carcinogenic. Azoreductase activity is commonly found in bacteria. Three types of azoreductases have been characterized. They are flavin dependent NADH preferred azoreductase, flavin dependent NADPH preferred azoreductase, and flavin free NADPH preferred azoreductase. This presentation will highlight how azo dyes are metabolized by commensal bacteria, mechanisms of azo reduction, structure and function of azoreductase, and the potential contribution in the carcinogenesis/mutagenesis of the reduction of the azo dyes.