Mycotoxins are secondary metabolites produced by mould fungi — toxic compounds that the mould releases into its environment as part of its competitive survival strategy against bacteria and other organisms. They are not the mould itself. They are what the mould produces, and they are considerably smaller and more mobile than mould spores — capable of penetrating deeply into the respiratory tract, crossing biological membranes, and accumulating in tissue in ways that spores cannot.
The health effects of acute, high-level mycotoxin exposure have been known for centuries — ergotism from contaminated rye, aflatoxin-related liver failure from contaminated groundnuts. What is less established in conventional medicine, and considerably better established in functional medicine research, is the clinical picture of chronic low-level mycotoxin exposure from living or working in water-damaged buildings. This is the exposure pattern that is relevant for most people asking about mould illness — not an acute toxic event, but a sustained background exposure that over months and years produces a constellation of symptoms that looks like no single recognisable disease because it is not one.
The Mycotoxins Most Relevant to Indoor Exposure
Ochratoxin A (OTA)
The most commonly detected mycotoxin in urine testing of people with mould illness. A nephrotoxin — it accumulates in kidney tubule cells, impairing renal function and the kidney's role in detoxifying other compounds. Also immunosuppressive and genotoxic. Found in water-damaged buildings and in dietary sources including stored grains, coffee, dried fruit, and wine.
Trichothecenes
Among the most toxic mycotoxins relevant to indoor environments. Stachybotrys — the notorious black mould — produces trichothecenes that are potently immunosuppressive, inhibit protein synthesis, and cause significant mucosal membrane damage. Particularly associated with severe, treatment-resistant mould illness presentations. Capable of dermal absorption, not just inhalation.
Aflatoxins
Primarily dietary — contaminated peanuts, tree nuts, maize, spices. Indoor building exposure is less common than dietary exposure. Potently hepatotoxic and among the most carcinogenic naturally occurring compounds known. Relevant particularly in people with both building exposure and high consumption of high-risk foods.
Gliotoxin
A potent immunosuppressive mycotoxin produced by Aspergillus fumigatus — the species most associated with invasive aspergillosis in immunocompromised individuals. Gliotoxin suppresses neutrophil and macrophage function, impairing the innate immune response to the organism producing it. Relevant in people with Aspergillus colonisation of the airways alongside building exposure.
Zearalenone
A mycoestrogen — it binds oestrogen receptors and exerts oestrogenic effects in tissue. Relevant as a potential contributor to oestrogen dominance and hormonal disruption in people with dietary or environmental Fusarium exposure. The DUTCH oestrogen metabolite pattern in mould-exposed individuals sometimes shows unexplained oestrogen elevation that dietary and liver-based explanations do not fully account for.
Citrinin and Enniatins
Less commonly discussed but increasingly detected in comprehensive mycotoxin urine panels. Citrinin is nephrotoxic and often found alongside ochratoxin A, amplifying its renal effects. Enniatins are emerging contaminants in grains with ionophoric properties — they disrupt cellular ion gradients, impacting mitochondrial function.
The Clinical Picture — Why It Gets Missed
Mould-related illness is missed consistently by standard investigation for a straightforward reason: standard blood panels, urine tests, and imaging do not include mycotoxin measurement. A GP ordering a full blood count, metabolic panel, thyroid, and inflammatory markers for someone with chronic fatigue and brain fog will find nothing specific — because mycotoxins do not show up on these tests, and the downstream effects they produce (immune dysregulation, mitochondrial impairment, neuroinflammation, gut barrier compromise) each look like something else when examined individually.
Common presentations
Pattern clues that suggest mould
The single most useful clinical question in a mould illness assessment: do your symptoms improve significantly when you are away from your home or workplace for three or more consecutive days? A clear yes is the most clinically significant piece of evidence available — more meaningful than any test result — because it identifies the exposure source before testing confirms what is causing the problem.
The Genetics of Susceptibility — Why Not Everyone in the Building Is Ill
A common barrier to taking mould illness seriously — from patients, families, and practitioners — is the observation that other people in the same building are not symptomatic. If the building were causing illness, surely everyone would be affected?
The answer lies in the genetics of mycotoxin clearance. Approximately 24% of the population carry HLA-DR variants — human leukocyte antigen subtypes — that impair their ability to produce antibodies against certain biotoxins, including mycotoxins. In people with these variants, mycotoxins that enter the body are not adequately tagged for immune clearance. They recirculate, accumulate in tissue, and trigger chronic immune activation without resolution. In people without these variants, the immune system tags and clears the mycotoxins more efficiently, and significant symptoms may not develop even in the same level of exposure.
This is not a weakness or a disease. It is genetic variation in the immune response to a class of toxins that most human evolutionary history did not encounter in the concentrations produced by modern water-damaged building materials. The HLA-DR typing test identifies susceptibility. It does not diagnose mould illness — it explains why some people are affected and others in the same environment are not.
The Connection to Glyphosate and Combined Toxic Burden
Mycotoxins and glyphosate share a clinically important interaction that is worth understanding. Glyphosate — the active ingredient in Roundup — disrupts the cytochrome P450 enzyme system in the liver, impairing Phase One detoxification capacity. A person with glyphosate burden has reduced capacity to metabolise and excrete mycotoxins. The mycotoxins that might otherwise be processed and cleared accumulate more readily in someone whose detoxification system is already compromised.
This combined burden explains why some people in modern environments develop multi-system illness that neither mycotoxin testing nor glyphosate assessment fully explains in isolation. The Organic Acids Test glyphosate add-on alongside a comprehensive mycotoxin urine panel gives a more complete toxic burden picture than either alone. And the clinical approach — supporting Phase One and Phase Two detoxification, restoring glutathione (consumed by both), addressing gut dysbiosis driven by both — overlaps significantly between the two presentations.
What Testing Reveals
The Clinical Approach — What Has to Come First
The most important principle in mould illness management is one that many practitioners and patients resist because it is inconvenient: no clinical intervention will produce durable recovery if the exposure continues. Supplements, binders, detoxification protocols, and immune support are all significantly compromised in their effect if the person returns daily to a mouldy building. The mycotoxin burden cannot be reduced faster than it is being topped up.
This means that building assessment and remediation — or relocation — is the clinical first step, not the last resort. It is often the most practically difficult step. Remediation is expensive. Relocation is disruptive. But without it, the clinical work is palliative rather than curative. This is a conversation that needs to happen at the beginning of the clinical engagement, not after months of treatment that fails because the source has not been addressed.
The Recovery Protocol — The Correct Sequence
Once exposure is addressed, recovery follows a specific sequence. Not the wrong sequence, which produces partial results. The right one.
First: binders. Mycotoxins undergo enterohepatic recirculation — they are excreted through bile into the gut and reabsorbed before they can leave the body. Binders — cholestyramine (pharmaceutical), activated charcoal, bentonite clay, zeolite, and GI Detox formulations — interrupt this reabsorption by binding mycotoxins in the gut before they can be reabsorbed. This is not optional in an active mycotoxin burden situation. Without binders, the detoxification system processes the same mycotoxin repeatedly without achieving net clearance.
Second: gut restoration. The gut ecology disrupted by mycotoxin exposure — Candida overgrowth, reduced commensals, compromised barrier — must be addressed using the standard gut restoration protocol. The GI-MAP guides which organisms need addressing. Cholestyramine and other pharmaceutical binders should be separated from probiotics and oral supplements by at least two hours as they will bind these as well.
Third: glutathione and antioxidant support. NAC, liposomal glutathione, and alpha lipoic acid support the oxidative burden of mycotoxin clearance. Glutathione is consumed by mycotoxin conjugation — the same mechanism as heavy metals — and must be actively supported during the clearance phase.
Fourth: immune recalibration. Once the mycotoxin burden is reducing, the chronically activated innate immune system needs support to down-regulate from the inflammatory state it has been sustaining. This is where specific immune-modulating approaches — VIP (vasoactive intestinal peptide, in the Shoemaker protocol), adaptogenic herbs, and ongoing gut work — become relevant.
Do your symptoms improve significantly when you spend several consecutive days away from your home or workplace? This is the most sensitive clinical indicator — more discriminating than any single test result.
When did your symptoms begin, and did anything change in your living or working environment around that time? People rarely connect a property change with a health change — particularly when the symptoms develop gradually over months.
Have you or other occupants noticed visible mould, persistent damp, water staining, or a musty smell? Absence of visible mould does not exclude significant mould burden — the most toxic species (Stachybotrys) grow in wall cavities and behind plasterboard, invisible until significant structural damage has occurred.
Are other people in the building affected? Others being unaffected does not exclude building-related illness — HLA-DR susceptibility means that one occupant may be significantly affected while others are not. But others with similar symptoms strongly supports a building source.
Mould illness sits at an uncomfortable intersection between mainstream medicine — which does not have a framework for it — and functional medicine — where it is increasingly recognised but remains incompletely researched. The clinical reality, in practice, is that a significant proportion of people with treatment-resistant chronic fatigue, brain fog, multi-system symptoms, and multiple failed diagnoses have a building exposure history that has never been seriously investigated. The testing exists. The clinical framework exists. The gap is clinical curiosity about the environment rather than the standard panel.
As with every presentation that standard investigation misses: test, don’t guess. And before testing, ask the question that the standard clinical consultation never asks — where do you spend your time, and what does that building look like?