Three genera of molds produce the vast majority of mycotoxins that affect human health: Aspergillus, Fusarium, and Penicillium. Several less common genera, including Alternaria, Stachybotrys, and Claviceps, also produce harmful toxins. Each of these molds thrives in different environments, targets different crops or materials, and generates distinct toxins with specific health effects.
Aspergillus: The Aflatoxin Producer
Aspergillus species are responsible for two of the most dangerous mycotoxin families: aflatoxins and ochratoxins. Aflatoxin B1, produced primarily by Aspergillus flavus and Aspergillus parasiticus, is the most potent natural carcinogen known. The International Agency for Research on Cancer classifies aflatoxins as Group 1 carcinogens, meaning there is clear evidence they cause cancer in humans. Even in small amounts, aflatoxins are genotoxic, capable of directly damaging DNA. Large doses can cause acute poisoning called aflatoxicosis, which is sometimes fatal due to severe liver damage. Chronic low-level exposure has been linked to liver cancer and impaired growth in children.
Several Aspergillus species also produce ochratoxin A, including A. ochraceus, A. carbonarius, A. niger, and A. alliaceus. Ochratoxin A primarily damages the kidneys and has been linked to tumors in the human urinary tract. It also suppresses the immune system and can interfere with fetal development. The IARC considers it a possible human carcinogen.
Aspergillus molds commonly contaminate stored grains, peanuts, tree nuts (especially pistachios and Brazil nuts), corn, and coffee beans. The FDA maintains specific action levels for aflatoxin in these foods and routinely tests products like peanuts, milk, and pistachios for contamination. Aflatoxin M1, a metabolite that passes into the milk of animals fed contaminated grain, is regulated separately in dairy products.
Fusarium: Toxins From the Field
Fusarium species are the dominant mycotoxin producers in cereal crops like wheat, barley, and corn. Unlike Aspergillus, which typically contaminates food during storage, Fusarium tends to infect plants while they’re still growing in the field. This genus produces three major families of mycotoxins: trichothecenes, fumonisins, and zearalenone.
Trichothecenes are divided into four types. The most commonly encountered are deoxynivalenol (often called “vomitoxin” for its effects) and T-2 toxin. Deoxynivalenol causes severe gastrointestinal symptoms in humans, including nausea, vomiting, and diarrhea. T-2 toxin is more potent, with immunosuppressive, cytotoxic, and carcinogenic properties. Other trichothecenes produced by Fusarium include nivalenol, which suppresses immune cell mobility and may increase mutation rates, and fusarenon X, which is both cytotoxic and immunosuppressive.
Fumonisins, particularly fumonisin B1, contaminate corn more than any other crop. They are considered potential carcinogens and have been linked to disruption of the intestinal barrier, immune system changes, and poor fetal development. Zearalenone, the third major Fusarium toxin, mimics estrogen in the body and primarily affects reproductive systems in livestock, though it also appears in human food supplies through contaminated grains.
Penicillium: Ochratoxin and Patulin
While Penicillium is perhaps best known for producing the antibiotic penicillin, certain species generate harmful mycotoxins. Penicillium verrucosum and Penicillium nordicum produce ochratoxin A, particularly in cooler climates where Aspergillus species are less active. This makes Penicillium the primary source of ochratoxin A contamination in European grain and cured meat products.
Penicillium expansum produces patulin, a toxin most commonly found in apples and apple-based products like juice and cider. Patulin causes acute damage to the liver, kidneys, and spleen, and suppresses immune function. Citrinin, another Penicillium-derived toxin, is a kidney toxin historically associated with yellowed rice disease in Japan.
Stachybotrys: The Indoor “Black Mold”
Stachybotrys chartarum, commonly called “black mold,” grows on water-damaged building materials like drywall, ceiling tiles, and wallpaper. It produces satratoxins, a type of macrocyclic trichothecene that is among the most potent toxins in the trichothecene family. Satratoxins block protein production in cells and trigger both inflammation and cell death.
In heavily contaminated water-damaged homes, airborne satratoxin concentrations have been measured at levels ranging from 2 to 330 nanograms per cubic meter. Animal studies show that inhaling satratoxin G damages sensory neurons in the nose and causes inflammation in the brain. Stachybotrys grows more slowly than other indoor molds, but when it establishes itself on chronically wet materials, it can produce toxins continuously for long periods.
Alternaria and Claviceps
Alternaria alternata, a common outdoor mold that also grows on grains and fruits, produces several toxins including alternariol and altenuene. These toxins tend to be less potent than aflatoxins or trichothecenes, but Alternaria grows at a wider range of temperatures, producing toxins at temperatures as low as 5°C (41°F) when moisture is high enough.
Claviceps purpurea infects rye and other cereal grains, producing ergot alkaloids. These toxins cause ergotism, a condition that historically caused mass poisonings in medieval Europe. Ergot alkaloids constrict blood vessels and can cause hallucinations, gangrene, and convulsions. Modern grain processing has largely eliminated ergotism, though low-level contamination still occurs.
Conditions That Trigger Toxin Production
Not every mold colony produces mycotoxins. Toxin production depends heavily on moisture and temperature. The key measurement is water activity, a scale from 0 to 1 that reflects how much moisture is available to the mold. Peak mycotoxin production typically occurs at a water activity of 0.98 and a temperature around 25°C (77°F). At a water activity of 0.90, which corresponds to moderately dry conditions, toxin production drops to trace amounts or stops entirely.
This has practical implications. Properly dried grains stored in low-humidity environments produce far fewer mycotoxins than crops harvested wet or stored in damp conditions. In buildings, controlling moisture through ventilation, dehumidification, and prompt repair of leaks is the most effective way to prevent toxin-producing mold growth. Temperature matters too, but moisture is the more critical variable. Some molds, like Alternaria, can produce toxins even at refrigerator temperatures if the substrate is wet enough.
Which Foods Are Most Affected
Mycotoxin contamination spans a wide range of agricultural products. Corn is vulnerable to aflatoxins, fumonisins, and trichothecenes. Wheat and barley are primary targets for Fusarium toxins like deoxynivalenol. Peanuts, pistachios, and Brazil nuts are frequently tested for aflatoxin. Coffee beans, spices, and soybeans can harbor multiple types of mycotoxins depending on growing and storage conditions.
Dairy products carry a specific risk: when cows eat aflatoxin-contaminated feed, a metabolite called aflatoxin M1 passes into their milk. This is why regulatory agencies test milk separately from other food products. Apple juice and cider are the primary concern for patulin contamination, since Penicillium expansum commonly infects bruised or damaged apples.
Regulatory agencies set limits measured in parts per billion for the most dangerous mycotoxins. The FDA publishes specific action levels for aflatoxins in foods, peanuts, tree nuts, and milk. The European Union generally sets stricter limits than the United States and regulates a broader range of mycotoxins, including deoxynivalenol, zearalenone, and ochratoxin A in various food products.
How Mycotoxins Affect the Body
Different mycotoxins target different organs, but the liver and kidneys bear the heaviest burden. Aflatoxins are primarily hepatotoxic, meaning they damage the liver. Ochratoxin A is nephrotoxic, targeting the kidneys. Trichothecenes tend to affect the gut lining and suppress the immune system. Many mycotoxins share overlapping effects: DNA damage, immune suppression, and interference with normal cell growth.
Exposure happens mainly through eating contaminated food, though inhalation is the primary route for indoor molds like Stachybotrys. Chronic low-level dietary exposure is more common than acute poisoning in developed countries, where food testing catches the worst contamination before it reaches consumers. In regions with less robust food safety infrastructure, acute aflatoxicosis outbreaks still occur, sometimes affecting hundreds of people at once.