Sterigmatocystin

Sterigmatocystin is a poison of the type dermatoxin, from the fungi genus aspergillus. It appears on crusts of cheese with mold.

Health risk
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. 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.