mycotoxin, naturally occurring metabolite produced by certain microfungi (i.e., molds) that is toxic to humans and other animals. Mycotoxins occur in great number and variety, though only a small number occur regularly in human foodstuffs and animal feeds. Foods that may be affected include barley, corn, groundnuts, oats, rice, rye, sorghum, sugar, and wheat. Mycotoxins generally are distinguished from mushroom poisons, which are produced by large fungi (i.e., mushrooms).

Mycotoxins of particular importance to the health of humans and livestock include aflatoxins, deoxynivalenol/nivalenol, fumonisins, ochratoxin, and zearalenone. The toxic effects of such substances can include hallucinations, skin inflammation, severe liver damage, hemorrhages, abortion, convulsions, neurological disturbances, and death in livestock and humans. Several mycotoxins cause DNA damage or are associated with tumour formation. Deoxynivalenol, for example, which is produced by certain species of Fusarium, is genotoxic, inducing DNA damage and significantly increasing apoptosis rates in cells. Aflatoxins, which are a complex of mycotoxins produced by species of the soil saprophyte Aspergillus, can cause liver disease and have been shown to be potent carcinogens (cancer-causing agents) in laboratory animals.