Carcinogens are chemical substances, mixtures, natural products, physical agents (sunlight, radioactivity, etc), industrial products and occupations that have different levels of cancer-causing potential. The majority of carcinogens are of environmental origin and most of them can cause cancer after prolonged and high levels of exposure. The first environmental carcinogens were connected with various occupations where workers were exposed during their working lives (such as asbestos, benzene, leather products, etc.). A great number of carcinogens were identified in the last century, such as tobacco smoke, urban air suspended particulates and industrial products (polychlorinated pesticides, polychlorinated biphenyls, vinyl chloride, etc.). A number of carcinogens of natural origin were discovered in various foods, such as tannic acid, safrole, pyperadine and alpha-methylpyrroline in black pepper, aflatoxins and ochratoxin A made by fungal food contaminants. Cooking and frying produce carcinogenic heterocyclic amines in cooked meats and some highly mutagenic compounds such as polycyclic aromatic hydrocarbon. Cancer is a disease characterised by “damaged” or mutations of cellular DNA and uncontrolled growth of altered cells into neoplastic tumors. This review explains in simple terms the present knowledge on carcinogenic substances and factors, the methodology for their classification by international and national scientific organizations, the mechanisms of carcinogenic potential. The review presents the most important causes of cancer and the regulations for the protection of workers, consumers from carcinogenic exposure and the environmental problems from chemical pollutants with hazardous carcinogenic properties.

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