The Mold in Roquefort Could Make You Sick. It Doesn't.

Penicillium roqueforti, the fungus that turns curd into Roquefort, Stilton, and Gorgonzola, is technically capable of poisoning you. In a Petri dish on the right substrate it produces PR toxin — a sesquiterpene that has been linked to mycotoxicoses in livestock — along with the neurotoxin roquefortine C and a handful of other secondary metabolites. The American mycologist Charles Thom formally described the species in 1906; the toxin profile was worked out across the second half of the twentieth century.

None of that lands on your cheese plate in any meaningful dose. Inside a wheel of blue, the fungus is operating in a low-oxygen, salt-heavy, mildly acidic environment, which is exactly the wrong recipe for PR toxin biosynthesis. What little PR toxin does form is unstable: it degrades inside the cheese matrix into PR imine, a far less toxic compound. Roquefortine C accumulates a bit more, but the concentrations measured in commercial blue cheese are orders of magnitude below anything that has shown an effect in mammals.

The industry also stacks the deck. Dairies don't culture wild strains; they pick lineages that, generation after generation, produce less of the offending metabolites. A 2023 review in npj Science of Food tracked how domesticated P. roqueforti lines have diverged from wild ones, with mycotoxin output among the traits selected against.

Which means a soft pile of veined Roquefort is the rare case where the disclaimer — "this organism makes a neurotoxin" — is true and irrelevant at the same time.