Mycotoxins: What They Are, the Basics Explained Clearly
A word that comes up more and more often in forums and practices, yet that hardly anyone gets really explained. Here you get the basics. Calm, clear, without fear.
Mycotoxins are the toxins that some molds produce. Not the fungus itself, but its chemical legacy. They are found in food and in damp buildings, enter you through eating and breathing, and with chronic exposure can challenge several body systems at once.
Before you concern yourself with tests, detoxification or individual mold species, you need a clear picture of the basic question: what are mycotoxins in the first place?
This article is the calm entry point into the whole topic. No technical jargon without translation. No scaremongering. Just the foundation on which everything else builds.
How I label evidence in this article
Much of what we know about the effects of mycotoxins comes from cell and animal models. Human studies exist, but they are limited. With every statement I transparently mark how robust the data are.
When the term comes up for the first time
A woman in her mid-forties, office work, comes in with a folder full of unremarkable findings. Fatigue that sleep does not take away. A head as if wrapped in cotton wool. Fluctuating abdominal complaints that no meal plan explains.
In a calm review of the past years, a detail surfaces that no one had ever asked about: a water damage in the bedroom some time ago, superficially dried, never properly remediated. She had barely had it on her radar herself.
The word "mycotoxins" she had previously read only once on the internet and immediately dismissed, because it sounded like conspiracy. It is not. It is biochemistry.
Clarification: This is an anonymized, typical pattern from practice, not an individual case report. A temporal connection between environment and complaints is a clue, not proof of a cause. Such connections belong to careful medical evaluation.
What mycotoxins really are
Let us start right at the beginning. The word is made up of two parts. "Myco" comes from the Greek word for fungus. "Toxin" means poison. So mycotoxins are simply fungal poisons.
More precisely: mycotoxins are toxic metabolic products that some molds produce. The fungus does not produce them for fun. It uses them as chemical weapons. With them it keeps bacteria and competing fungi at bay, so as to have its food to itself.
Here is an image that makes a lot of it clearer. Picture a mold like a tiny factory. The fungus is the factory, alive and growing. The mycotoxins are what the factory emits. And the crucial point: these substances remain, even when the factory has long since closed. Mycotoxins are chemically stable molecules. They are not a living being. You can kill a fungus, wipe it away, treat it with heat, and the toxin is still there.
Mold is the fungus. Mycotoxins are its poisons. That is not the same thing, and the difference matters in practice. You can be exposed to mycotoxins without a fungus growing anywhere inside you. And not every mold even forms notable amounts of mycotoxins. How much arises depends on the fungal species, the moisture, the substrate and time.
Today more than 400 different mycotoxins are known. Sounds like a lot, and it is. For practice, however, only a handful are really important. Those are exactly the ones we will look at in a moment.
And now you know why "mold wiped away, so all is well" falls short. The visible factory is gone, the invisible legacy can remain.
The six most important mycotoxins at a glance
You do not have to memorize 400 names. These six are enough to understand the field. Each has a typical character, almost like a personality.
The one with the clearest stamp
Formed above all by Aspergillus flavus. It is the only mycotoxin that IARC classifies as Group 1, that is, as an established human carcinogen. Mainly an issue with contaminated foods such as peanuts and corn, less so in the living space.
The one for kidney and brain
Formed by Penicillium and Aspergillus. In laboratory models it burdens kidney and nerves. OTA can cross the blood-brain barrier. It is found in grain, coffee and dried fruit as well as in damp indoor spaces. Classified by IARC as Group 2B, that is, not established in humans.
The fast and harsh one
Belongs to the trichothecenes, formed above all by Fusarium, indoors also by black mold (Stachybotrys). In models it is considered highly potent, inhibits the cell's protein production and can strongly dampen the immune system.
The one for the gut
Also called "vomitoxin", likewise a trichothecene from Fusarium. One of the most common mycotoxins in grain worldwide. In cell and animal models it can disturb the gut barrier and trigger nausea.
The false estrogen
From Fusarium. In its shape it resembles the hormone estrogen so closely that it binds to the same docking sites. The body "reads" a hormonal message that is not a real one. Clearly documented in animal models, human data limited.
The cloaking agent
Formed by Aspergillus fumigatus. In laboratory models it acts immunosuppressively, so it can slow down defense cells. With this the fungus gains some respite from the immune system. Relevant above all when defenses are weakened.
"Mycotoxins" sounds like a single, threatening thing. In truth it is a whole family of very different substances. Some are strictly regulated and well researched, others barely at all. Some concern mainly food, others mainly damp walls. Whoever breaks the field down into individual characters loses the diffuse fear and gains orientation.
Where mycotoxins form
Mold is no accident. It needs three things, always the same: moisture, something to feed on, and time. Where these three come together, it can grow. And where it grows, mycotoxins can form. There are two big settings.
Setting one: your food
This is historically the oldest and best-researched place. Mycotoxins form in the field, in storage and in transport. Affected are above all starch- and oil-rich foods:
- Grains such as wheat, corn, oats, rye (often DON, ZEN, OTA)
- Nuts, especially peanuts and pistachios (aflatoxins)
- Coffee, cocoa, dried fruit (often OTA)
- Spices and some dried herbs
Important for context: in Europe there are strict statutory limits for mycotoxins in food, and they are monitored. That considerably lowers the typical exposure through food for most people. So it is no reason to be afraid before breakfast. It is a reason to consistently discard moldy food, instead of just cutting away the bad spot.
Noble mold on Camembert or in Roquefort is no problem. These are selected cultures that, under the usual conditions, do not form relevant amounts of harmful mycotoxins. The mold, on the other hand, that grows uninvited on the bread or the nuts belongs entirely in the bin. In soft foods the invisible toxins often migrate into apparently clean areas.
Setting two: your building
This is the setting that was long underestimated and today gets more attention. A water damage, a leak, poorly ventilated moisture, and mold finds ideal conditions behind wallpaper, in insulation, under floor coverings or in air conditioning systems.
The tricky thing about it: you do not have to see the mold to be exposed to it. Spores and tiny fragments of the fungus, to which mycotoxins can be bound, enter the room air as fine dust. You breathe them in without noticing. Indoors, above all Aspergillus, Penicillium and, with prolonged wetness, Stachybotrys (black mold) are relevant.
In 2009 the WHO summarized the data in its guidelines on indoor air. Living in damp, mold-burdened buildings is statistically associated with more respiratory complaints, asthma and allergies. The WHO estimated that a considerable proportion of existing asthma could be connected with home dampness and mold.
And now you know why the first question when there is suspicion is never "which pill?", but "where is the moisture?". The source rarely sits in the body. It sits in the environment.
How mycotoxins get into the body
There are three doors through which mycotoxins get into you. Which door is in the foreground depends on the setting.
Through the mouth: ingestion
The classic route with contaminated foods. The toxins enter the digestive tract via grain, nuts, coffee and the like. Here the gut is the first organ that comes into contact with them, and the liver the most important organ for breaking them down.
Through the air: inhalation
The decisive route in water-damaged buildings. Spores and fine particles with adhering toxins are inhaled and meet the sensitive mucous membranes of nose, sinuses and lung. This route partly bypasses the protective detour via liver and gut.
Through the skin: contact
The secondary route. Direct skin contact with heavily contaminated material plays a role above all in occupational exposure, for example in agriculture or building remediation. For everyday life it is usually less significant than food and breathing air.
Here it is worth a second look at the middle door. When you eat something, it runs through a built-in safety check: gut wall, then liver, which can neutralize a large part before the substance enters the circulation. With inhalation this first check is weaker. That is why a chronic exposure through breathing air in damp rooms can become clinically particularly relevant, even if the individual amount taken up seems small.
Your body is not a passive bucket. It has detoxification routes: the liver converts mycotoxins in two steps and makes them water-soluble, the bile and the gut excrete them, the kidney filters along. Among other things, the body's own antioxidant glutathione helps. As long as the burden is low and these routes run well, the body usually copes well. It gets tight with high chronic exposure or when detoxification is exhausted.
Why mycotoxins can be relevant to health
Now the question that probably brought you here. If the body has detoxification routes and there are limits, why do we even talk about it?
The answer lies in a property that many mycotoxins share: they do not attack a single organ, but often several systems at once. That is exactly what makes them clinically confusing. When a substance can pull at the nervous system, the immune system, energy production and hormone balance all at the same time, it fits into no single specialist's drawer. Patients wander from door to door, and each individual finding stays unremarkable.
Ratnaseelan and colleagues summarized in 2018 the data on mycotoxins, neuropsychiatric symptoms and immune processes. In cell and animal models several mycotoxins can trigger oxidative stress, inflammatory processes and effects on nerve cells. The authors emphasize that human data are still limited and that further research is needed.
What is important here is honesty about the data. A large part of what we know about mycotoxin effects comes from the test tube and from animal experiments. These show what a substance can do, under clearly defined conditions and often with higher doses. What that means for the individual person with low chronic exposure is harder to say. That is why I phrase it cautiously: mycotoxins can play a role, in some people, under certain conditions. It is not an explanation for everything, and it is no reason for fear.
The mycotoxin basics through the lenses of PNEI
In my practice I do not look at a single symptom, but at the interplay of the systems. Clinical Psychoneuroimmunology, PNEI for short, always asks: how does it all hang together? Here the four lenses, already at the basics level.
1. Nervous system
Some mycotoxins such as OTA can, in models, burden nerve cells and cross the blood-brain barrier. That could explain why those affected often report "brain fog", concentration problems and sleep disturbances. The complaints are not imagined.
2. Immune system
Mycotoxins show a double-edged immune effect in models. In some constellations they fire up inflammation, in others they dampen defenses (for example gliotoxin, T-2). Both directions can cause complaints.
3. Metabolism
The cell's power plants, the mitochondria, react sensitively to oxidative stress. When a lot of glutathione is consumed for detoxification, it is lacking elsewhere. That fits the picture of the deep exhaustion that sleep does not remedy.
4. Hormone system
Zearalenone resembles estrogen so strongly that it can occupy its docking sites. The lab may then measure normal values, while the body behaves differently. Hormonal messages can be distorted.
And now you know why a single blood value rarely suffices with this topic. It is a web, not a point. Whoever pulls only one thread overlooks the pattern.
"Maybe it is not about me, but about my surroundings."
For many people that is a liberating thought. Whoever has heard for years that everything is fine eventually blames themselves. To shift the question from "what is wrong with me?" to "what could be overloading my system?" not only takes off pressure. It also makes the problem workable.
Three calm steps if the topic concerns you
You do not have to tear down your apartment now or buy ten tests. Mycotoxins are no case for self-experiments following internet instructions. But there are three composed first steps.
Go through your environment honestly
Was there, or is there, water damage, damp corners, musty smells, visible mold in your apartment, at your workplace or in your car? Did something about your complaints begin in time with a move or a water situation? Do you feel noticeably better on holiday away from home? Those are the most valuable clues, and they cost nothing.
Do not fall into hyperactivity
The first reflex is often to want to "detoxify" immediately. That is understandable, but risky. Whoever sets off without a plan and without guidance can feel temporarily worse. The right order is always: first find the source and end the exposure, then everything else. Calmly, not in panic.
Seek a specialized medical history
When the clues thicken, a medical practice with a focus on environmental medicine and functional diagnostics is worthwhile. A thorough, time-intensive history that includes the environment is often the most valuable examination here. It puts in order what otherwise stays scattered.
A suspected mycotoxin exposure belongs in medical hands, not in a self-directed detoxification program. Binders, antifungal strategies and stronger measures can, in the wrong order or dosage, do more harm than good. Let yourself be accompanied, instead of experimenting.
How it continues in the cluster
This article was the foundation. If you want to go deeper, the following spokes build on it. You can read them in any order, depending on what concerns you right now.
The pillar: all systems, all mycotoxins, diagnostics and therapy in context.
Which Aspergillus species form which mycotoxins and when an evaluation makes sense.
The only mycotoxin in IARC Group 1: effect, sources and protection.
The mycotoxin with a particular connection to nerves and kidneys.
Frequently asked questions about mycotoxins
What are mycotoxins in simple terms?
Mycotoxins are toxic metabolic products that some molds produce. The fungus uses them as chemical weapons to keep competitors at bay. They are not living organisms but stable molecules that remain even after the fungus is long dead. More than 400 different mycotoxins have been described.
Are mold and mycotoxins the same thing?
No. Mold is the living fungus, mycotoxins are the toxins that some mold species produce. You can be exposed to mycotoxins without the fungus itself growing in your body. Not every mold forms mycotoxins, and the amount depends strongly on the species and growth conditions.
Which mycotoxins are the most important?
The ones that receive particular clinical attention are the aflatoxins (above all aflatoxin B1), ochratoxin A, the trichothecenes T-2 and deoxynivalenol (DON), zearalenone and gliotoxin. Aflatoxin B1 is classified by IARC as Group 1, meaning an established human carcinogen. The others are assessed differently depending on the substance.
Where do mycotoxins form?
In two main places: in food (grains, corn, peanuts, coffee, dried fruit, spices) and in damp or water-damaged buildings (behind wallpaper, in insulation, in air conditioning systems). Mold needs moisture, a food source and time. Where these three come together, mycotoxins can form.
How do mycotoxins get into the body?
Via three routes: through eating (ingestion via contaminated food), through inhalation (spores and particle-bound toxins in damp rooms) and to a lesser extent through the skin. In water-damaged buildings inhalation is in the foreground, with food it is ingestion.
Why can mycotoxins be relevant to health?
Several mycotoxins act in laboratory models and animal studies on the nervous system, immune system, mitochondria, liver and hormones. They often attack several systems at once, which can explain non-specific complaints. Human studies are limited but growing. In a subset of chronic complaints without a clear cause, an exposure could be an overlooked co-factor.
Can my body get rid of mycotoxins again?
Yes, the body has detoxification routes via liver, bile, gut and kidney. As long as the burden is low and detoxification works well, it usually copes well. It becomes difficult with high chronic exposure or when detoxification capacity is exhausted. The first and most important step is always to find the source and end the exposure.
Do I need to worry about every piece of blue cheese?
No. The noble molds in cheeses such as Camembert or Roquefort are selected cultures that, under the usual conditions, do not form relevant amounts of harmful mycotoxins. It is different with unintended mold on bread, nuts or fruit, which should be discarded completely.
When should I think about a mycotoxin exposure?
When you have a long history of complaints without a clear diagnosis, when there was or is water damage or visible mold in your living or working environment, and when complaints get worse at home and better on holiday. These signs justify a calm, specialized medical evaluation, not panic.
Sources and evidence notes
A large part of the knowledge about mycotoxin effects comes from cell and animal models. Human data exist, but are limited. I label transparently.
- Ostry V et al. Mycotoxins as human carcinogens, IARC classification update. Mycotoxin Research. 2017. doi:10.1007/s12550-016-0265-7 [agency document, review]
- WHO. Guidelines for indoor air quality: dampness and mould. 2009. WHO agency document [agency document, review]
- Ratnaseelan AM et al. Effects of Mycotoxins on Neuropsychiatric Symptoms and Immune Processes. Clinical Therapeutics. 2018. doi:10.1016/j.clinthera.2018.05.004 [in vitro, in vivo, review]
- Mendell MJ et al. Respiratory and Allergic Health Effects of Dampness, Mold, and Dampness-Related Agents. Environ Health Perspect. 2011. doi:10.1289/ehp.1002410 [systematic review, human]
- Chang C, Gershwin ME. The Science Behind Mold and Human Illness. Clin Rev Allergy Immunol. 2019. doi:10.1007/s12016-019-08741-0 [review]
Last updated: 16 June 2026.