Blue cheese is safe to eat for most people. The mold that gives it those distinctive blue-green veins is a deliberately introduced species called Penicillium roqueforti, which has been used in cheesemaking for centuries and is not the same as the mold that grows on forgotten leftovers in your fridge. That said, a few specific groups of people do need to be cautious, and proper storage matters.
Why the Mold in Blue Cheese Won’t Hurt You
Penicillium roqueforti can technically produce a potent toxin called PR toxin under laboratory conditions, but the chemistry inside a wheel of cheese neutralizes it. PR toxin is unstable and reacts rapidly with amino acids that are naturally present in high concentrations during cheese ripening. The breakdown products are far less toxic than the original compound. On top of that, the low-oxygen environment inside most cheeses doesn’t favor toxin production in the first place. Researchers have consistently found that cheese ripening conditions simply don’t allow PR toxin to accumulate.
Another compound, roquefortine, has been recovered from blue cheese at low levels, but no adverse health effects from eating the cheese have ever been reported. Mutagenicity testing on six commercial strains of Penicillium roqueforti found no mutagenic activity in either the fungus itself or the roquefortine it produces. In short, the EPA’s final risk assessment on this species concluded that normal production conditions do not pose a health concern.
Who Should Avoid Blue Cheese
While blue cheese is fine for the general population, three groups face real risks.
Pregnant women: The CDC lists soft blue-veined cheese made from unpasteurized milk as a riskier food choice during pregnancy because of the potential for Listeria contamination. Listeria can cross the placenta and cause miscarriage, stillbirth, or serious illness in newborns. The safer option, according to CDC guidelines, is to eat pasteurized soft cheeses heated to an internal temperature of 165°F or until steaming hot.
People taking MAO inhibitors: Blue cheese is high in tyramine, a compound that builds up naturally as protein-rich foods age. For most people, the body breaks tyramine down without issue. But if you take a type of antidepressant called an MAOI, your body can’t process tyramine efficiently. Eating high-tyramine foods like Stilton or Gorgonzola while on these medications can trigger a dangerous spike in blood pressure, sometimes severe enough to require emergency treatment. Symptoms include sudden severe headache, nausea, neck stiffness, chest pain, and vision changes. The Mayo Clinic notes that in rare cases, a severe spike can lead to stroke.
People with histamine intolerance: Blue cheese, like all aged and fermented foods, contains significant amounts of histamine. If your body has trouble breaking down histamine, even a small serving can trigger symptoms like headaches, flushing, hives, bloating, diarrhea, or a runny nose. Reactions vary widely from person to person. If you notice a pattern of these symptoms after eating aged cheeses, wine, or fermented foods, histamine intolerance is worth investigating.
Raw Milk vs. Pasteurized Blue Cheese
Many classic blue cheeses, particularly European varieties like Roquefort, are traditionally made with raw (unpasteurized) milk. In the United States, federal regulations have required since 1949 that any raw milk cheese be aged for at least 60 days before sale. After that period, the concentration of enzymes and salts in the cheese is considered sufficient to prevent harmful pathogens from growing.
Pasteurized blue cheeses carry a lower baseline risk because the heat treatment kills most dangerous bacteria before cheesemaking begins. If you’re in a higher-risk group (pregnant, immunocompromised, very young, or elderly), sticking with pasteurized versions or heating cheese thoroughly before eating is the more cautious route.
How to Tell When Blue Cheese Has Gone Bad
The tricky part with blue cheese is that it already looks and smells strong by design. The intentional mold runs in defined blue-green veins through the interior of the cheese. What you’re watching for is new, unwanted mold on the surface: fuzzy patches of white, pink, or grey that weren’t there when you bought it. These indicate contamination by a different organism.
Smell is another reliable signal. Blue cheese has a pungent aroma, but a sharp ammonia-like odor that’s noticeably stronger or different from what you’re used to suggests spoilage. If the texture has become slimy or excessively soft, that’s another reason to discard it. Once opened, blue cheese generally keeps in the refrigerator for one to two weeks when wrapped loosely enough to let it breathe but tightly enough to prevent excessive drying.
Potential Nutritional Upsides
Beyond safety, blue cheese contains a compound called spermidine that has attracted attention from researchers studying cardiovascular health. Spermidine appears to have a positive effect on heart muscle cells, and some researchers have pointed to it as one possible explanation for the so-called “French paradox,” the observation that cardiovascular disease rates in France are relatively low despite a diet rich in saturated fat. The exact mechanism isn’t fully understood, but the association between spermidine intake and reduced cardiovascular risk has been noted in multiple population studies.
Blue cheese is also a good source of calcium, protein, and certain B vitamins. It is, however, high in sodium and saturated fat, so portion size matters if you’re watching either of those. A typical serving is about one ounce, which is roughly the size of a pair of dice.