enzyme, while CYP3A4 is also active in human liver. The expression of CYP1A1 in human livers is low, less than 0,7% of the total hepatic CYP expression, while it contributes up to 12 to 30% in the oxidation of Sudan I in a set of human liver microsomes. Moreover, Sultan I strongly induces CYP1A1 in rats and human cells in culture, due to activation of the cytosolic aryl hydrocarbon receptor. In bladder tissue, CYP enzymes are not detectable, while there are relatively high levels of peroxidases expressed in these tissues. In addition to oxidation by CYP enzymes, Sudan I and its C-hydroxylated metabolites are also oxidized by peroxidases, such as a model plant peroxidase, but also by the mammalian enzyme, cyclooxygenase. As a consequence DNA, RNA and protein adducts are formed. (See figure 2). Therefore, peroxidase-catalyzed activation of Sudan I has been suggested, in a similar way to other carcinogens, such as the carcinogenic aromatic amines. It is suggested that a CYP- or peroxidase-mediated activation of Sudan I or a combination of both mechanisms as an explanation for the organ specificity of this carcinogen for liver and urinary bladder in animals. The Sudan I metabolites formed by peroxidase are much less likely to be formed at physiological conditions, because in vivo there are many nucleophilic molecules present which scavenge the Sudan I reactive species. Hence, formation of adducts of Sudan I reactive species with nucleophilic species, such as DNA, tRNA, proteins, polynucleotides, and polydeoxynucleotides seems to be the preferred reaction under physiological conditions, with deoxyguanosine as the major target for Sudan-I DNA binding, followed by deoxyadenosine. Effect on humans Sudan 1 is a compound being warned of for health hazards by the EU regulation. It may cause allergic skin reactions and irritation of the skin. Exposure to the skin can happen by direct exposure to textile workers or by wearing tight-fitting textiles dyed with Sudan 1. Allergic reactions are induced when the azo dye binds to the human serum albumin (HSA), forming a dye-HSA conjugate, which immunoglobulin E binds to, which causes a release of histamine. Sudan 1 is also suspected of causing genetic defects. The mutagenicity and genetic hazard has been evaluated with the Ames-test and animal experiments. Further it is more suspected of causing cancer. The carcinogenicity is estimated by animal testing. Safety and regulation The regulation of Sudan 1 in Europe started in 2003 after repeated notifications