A toxic substance with a low molecular weight, produced by certain moulds. Mycotoxins are secondary metabolites so are only produced when the mould is stressed in order to protect the spores. Conditions defined as ‘stressful’ vary depending on the species of mould but generally include increased levels of moisture and heat. Mycotoxins affect the health of both animals and humans. Over 500 mycotoxins have been discovered to date. Each mycotoxin affects the animal/human in a certain way, with some mycotoxins being carcinogenic, neurotoxic and immunosuppressive.