Sterigmatocystin is a mycotoxin of Aspergillus versicolor and Chaetomium species Sterigmatocystin is a poison of the type dermatoxin, from the fungi genus Aspergillus. It appears on crusts of cheese with mold. Sterigmatocystin is a toxic metabolite structurally closely related to the aflatoxins (compare general fact sheet number 2), and consists of a xanthone nucleus attached to a bifuran structure. Sterigmatocystin is mainly produced by the fungi Aspergillus nidulans and A. versicolor. It has been reported in mouldy grain, green coffee beans and cheese although information on its occurrence in foods is limited. It appears to occur much less frequently than the aflatoxins, although analytical methods for its determination have not been as sensitive until recently, and so it is possible that small concentrations in food commodities may not always have been detected. Although it is a potent liver carcinogen similar to aflatoxin B1, current knowledge suggests that it is nowhere near as widespread in its occurrence. If this is the true situation it would be justified to consider sterigmatocystin as no more than a risk to consumers in special or unusual circumstances. Sterigmatocystin is a number of closely related compounds such o-methyl sterigmatocystin are known and some may also occur naturally. The IARC-classification of sterigmatocystin is group 2B, which means it is possibly carcinogenic to humans. In practice, the risk is quite low however, because this substance only appears on cheese crusts with mold, and because of that the chance of daily exposure is very low. Sterigmatocystin is a molded crust is best not to be consumed in whole, but after removing the crust, the cheese can still be consumed. Sterigmatocystin is a different kind of mold than that which appears on cheese itself, which can simply be removed before further consumption.

Sterigmatocystin belongs to the family of Sterigmatocystins. These are phenolic compounds whose structure is based on the sterigmatocystin skeleton, a polycyclic aromatic moiety characterized by a furo[3',2':4,5]furan fused to a xanthen-7-one.