Mycotoxins Explained: The Real Danger Is Mostly on Your Plate

Mycotoxins are toxic chemical compounds some fungi produce. They're not the mold itself, and they're not produced by every mold, or even every strain of a toxin-capable species. Whether a given colony makes them depends on species, strain, food source, temperature and moisture.

The ones with the strongest evidence

Aflatoxins (from Aspergillus flavus and A. parasiticus) grow on corn, peanuts, tree nuts and cottonseed in warm, humid conditions. They're among the most potent natural liver carcinogens known and are classified by the IARC as Group 1 (carcinogenic to humans). In 2004 in Kenya, contaminated maize caused an outbreak of acute aflatoxin poisoning with well over 100 deaths. Food-safety regulators in most countries set legal limits and test grain and nut shipments for it.

Ochratoxin A turns up in cereals, coffee, dried fruit and wine; it is associated with kidney toxicity in animals and is classified as a possible human carcinogen (IARC 2B).

Ergot alkaloids come from Claviceps fungi growing on rye and other grains. Historical epidemics of ergotism ("St. Anthony's fire") caused gangrene and convulsions across medieval Europe.

Trichothecenes (including those made by Fusarium and Stachybotrys) and fumonisins (corn) also affect agriculture and food safety.

Food versus air

All the classic poisonings above involve eating mycotoxins at relatively high doses. Indoor air is a different route and different scale: the amount of mycotoxin on spores and fragments in typical moldy-building air is tiny compared with the doses in these food outbreaks. Occupational settings (grain handling, composting, farm work) with heavy dust exposure are where inhalation has clearer evidence, such as organic dust toxic syndrome.

What isn't known is whether chronic, low-level inhalation in damp buildings contributes to symptoms. That is an open research question, not a settled "yes" or "no". See Is "Toxic Mold" Real?.

Practical food rules

• Discard moldy bread, soft fruit, soft cheese, yogurt, jam, leftovers, nuts and grains: mold threads penetrate further than what you can see.
• Hard cheese and firm produce (carrots, cabbage): USDA guidance is to cut at least about 1 inch around and below the spot, keeping the knife out of the mold.
• Don't sniff moldy food; you're inhaling spores.
• Buy nuts and grain from reputable sources, store them cool and dry, and discard shriveled, discolored or bitter ones.
• Mold on intentionally cultured foods (blue cheese, salami casings, koji-based foods) is a managed, safe strain, a different thing entirely.

Why you'll hear the word everywhere

"Mycotoxin" is attractive marketing language. Be skeptical of products claiming to "detox mycotoxins" and of urine mycotoxin panels (see Mold Testing: What Works). The toxins are real. The commercial claims around them often outrun the evidence.