Could My Gut Issues Be Coming From Mould?

Key takeaways

• If your gut issues have not settled despite doing everything “right”, it is worth asking about where you live and work — not just what you eat. A history of a water-damaged building is an easily missed factor.
• Most mould-related exposure happens in two ways: damp indoor spaces, and small amounts of mould by-products called mycotoxins in food. This article focuses on the building route, because that is where the questions usually start.
• In cell and animal studies, several mycotoxins consistently damage the gut lining, thin its protective mucus layer, and shift the balance of gut bacteria.
• What we do not yet have is a human trial confirming the same at everyday exposure. So this is a case built on mechanism plus clinical experience.
• In clinical practice, a pattern comes up repeatedly: people with stubborn SIBO or gut symptoms who have already tried everything often turn out to share a history of a water-damaged home or workplace.
• Symptoms overlap heavily with many other conditions, so guesswork is unreliable. For the right person, a urine mycotoxin test — read by a practitioner alongside your history and symptoms — can add a useful piece to the picture.

If you have ongoing gut symptoms that will not settle, you may have started to wonder whether mould could be involved — particularly if you know, or suspect, that a home or workplace has had a damp or water problem. It is a fair question, and an under-asked one. Most gut advice starts and ends with food. But the environment you spend your days and nights in is part of your gut’s world too.

This article takes the middle path between the two extremes you will find online: the voices that dismiss mould entirely, and those that blame it for everything. We will look at what the science actually shows, where it is strong, and where it is still early. The aim is to help you think clearly about a real possibility — not to alarm you.

What do we actually mean by “mould” and “mycotoxins”?

Mould is a type of fungus that grows almost everywhere in nature. Mycotoxins are toxic compounds that certain moulds produce. Small amounts of both are a normal part of life. The problem is not the odd spore — it is heavier or ongoing exposure.

When people talk about mould and health, they usually mean one of two things.

Mould in buildings. This grows when surfaces or structures stay wet for long periods — a slow leak, rising damp, a flat roof that never quite dries, or condensation in a poorly ventilated room. The World Health Organisation notes that damp and mould indoors involve hundreds of species of fungi and bacteria that grow wherever there is enough moisture [1]. The dark, spreading growth many people call “black mould” (Stachybotrys chartarum) is one of these species, alongside other common indoor genera such as Aspergillus and Penicillium — but it is the dampness itself, rather than any single species, that best predicts health risk [1].

Mould in food. Certain moulds produce mycotoxins that can end up in the food chain — in grains, nuts, dried fruit, coffee and spices, especially when crops are stored warm or damp. Low-level food exposure is common and closely monitored by food safety bodies [2]. This route matters, but it is not our focus here, and it is worth being clear why.

How would mould from a building reach my gut?

Mould reaches your gut two ways: you swallow spores and mycotoxin fragments directly, or you inhale them. In a water-damaged building, this becomes repeated, cumulative exposure — day after day, in a space you can’t easily leave — rather than a single trace dose.

Food is the most direct route and the best measured. Mycotoxins you swallow pass straight through your digestive tract. But everyday food exposure is also low-level and widespread — in one European dataset, the mycotoxin deoxynivalenol turned up in 43.5% of food samples tested [2], and human biomonitoring routinely finds trace mycotoxins in the urine of healthy people [3]. Because it is so common, food exposure alone is a weak explanation for one person’s symptoms.

A water-damaged building is a different kind of exposure. Here, the issue is not a trace amount you ate once — it is repeated, cumulative exposure to spores, fragments and microbial by-products in the air of a space you cannot easily leave, day after day, often for months or years. This route is harder to measure, and its gut effects are far less studied than its effects on the airways. But it is exactly this ongoing, live-in exposure — rather than the occasional mouldy strawberry — that people are usually asking about when they wonder whether mould is affecting them.

So while food is the tidier research story, the building is the more relevant question for someone with persistent, unexplained symptoms and a damp history.

What does the research say about damp buildings and health?

The WHO’s review of the evidence found sufficient evidence linking indoor damp and mould with respiratory symptoms, respiratory infections, worsening of asthma, and effects on the immune system [4]. Crucially, the WHO was clear that the link cannot be measured precisely, and that no safe threshold for contamination could be set [4].

That immune finding is the important one for the gut question, even though the WHO review itself is not about the gut. The gut lining and the immune system are deeply intertwined. If a live-in exposure keeps the immune system on higher alert, it is reasonable to ask what that does downstream — including in the gut. The WHO evidence does not prove a gut effect. But it establishes that damp buildings are not harmless, and that they act partly through the immune system. That is the doorway the gut research walks through.

What do cell and animal studies show about mycotoxins and the gut?

In cell and animal studies, a consistent group of mycotoxins disturbs the gut barrier:

• Deoxynivalenol
• Ochratoxin A
• Zearalenone
• Fumonisin B1
• Aflatoxin B1
• Patulin

Across reviews, these compounds are linked to [5][6]:

• Direct damage to tight junction proteins — the “seals” between the cells lining the gut
• Thinning of the protective mucus layer over the gut lining
• Oxidative stress and inflammation in the gut lining
• Disruption of the stem cells that repair and renew the gut lining [7]

Here’s the mechanism in plain terms. Your gut lining is a single layer of cells held together by tight junction proteins. It works as a smart barrier: nutrients through, bacteria and toxins held back. Sitting over it is a protective mucus layer. When this system loosens, more bacterial fragments and toxins can cross into the body — what people loosely call “leaky gut”. Once the barrier loosens, bacterial fragments such as lipopolysaccharide cross more easily, which can drive low-grade inflammation throughout the body [8].

The microbiome takes a hit too. Ochratoxin A, for example, has been shown to shift the balance of gut bacteria and damage the gut lining [9]. The relationship runs both ways: gut microbes also break down and modify mycotoxins, which may help explain why two people with similar exposure respond very differently — a robust, diverse microbiome appears better able to cope than a depleted one [10].

So the mechanistic case is strong and consistent. Now the honest caveat, which matters as much as the findings: most of this work uses cells in a dish or animals, sometimes at doses higher than a typical daily intake. That does not make it irrelevant — mechanisms this consistent are a serious reason to investigate. But it means we should treat this as a compelling reason to look, not as proof that mould is driving any individual’s symptoms.

The pattern I keep seeing: stubborn gut symptoms and water-damaged buildings

In clinical practice, a pattern comes up again and again: clients with stubborn SIBO or gut symptoms who have genuinely tried everything — elimination diets, rounds of supplements and herbal antimicrobials, fasting protocols, stress work, vagus nerve exercises — and things still won’t fully resolve. When we widen the lens and ask about their environment, many turn out to have lived or worked in a water-damaged building.

Now, this is a clinical observation (that many clinicians have seen) and a working hypothesis, not settled science. Over the years, a large part of my work has shifted towards mould-related illness — not because I went looking for it, but because it kept finding me.

This is not proof of cause. People who have “tried everything” are, by definition, a complicated group, and there are always other factors in play. But it is a pattern common enough that I now ask about damp and water damage early — and I would encourage you to ask yourself the same question if your gut has been unusually resistant to treatment.

There are plausible mechanisms behind it. SIBO — too many bacteria in the small intestine, where numbers should be low — often traces back to slow gut motility, the natural cleaning wave that sweeps bacteria onward between meals [11][12]. If mycotoxins irritate and inflame the gut, it is reasonable to ask whether they could blunt that wave. There is a nutrient angle too: in human intestinal cells, deoxynivalenol (a mycotoxin) blocked key sugar transporters [13], and more recent animal work found it reduced glucose transport while driving inflammation [14]. If sugars are absorbed less efficiently high up in the gut, more may be left to feed bacteria further along. Sensible mechanisms — not proof, but reason enough to assess directly.

If your symptoms fit SIBO, it makes sense to test for it specifically. Healthpath’s SIBO Test uses a hydrogen and methane breath test and pairs the result with a practitioner review.

What about chronic fatigue, and the gut overlap?

People whose illness sits at the mould end of the spectrum rarely have gut symptoms alone. Fatigue, brain fog and a wider “unwell” picture often travel with the gut complaints, and there is overlap with chronic fatigue syndrome (CFS/ME), which itself frequently co-occurs with IBS-type gut symptoms.

One often-cited study here is Brewer and colleagues (2013), who detected at least one mycotoxin in the urine of 104 of 112 CFS patients (93%), and linked this to histories of water-damaged buildings [15]. It is a thought-provoking finding. Partly because many of these CFS patients, as we’d expect, reported numerous gut related symptoms too.

So I include it not as proof, but as an honest signal: experienced clinicians treating complex, multi-system illness keep bumping into the same association between mycotoxins, water-damaged buildings and unwell, gut-affected patients. Weak individual studies, a consistent clinical picture, and strong mechanisms — that is genuinely where this field sits right now.

What is CIRS, and is it a real diagnosis?

You may come across the term CIRS — Chronic Inflammatory Response Syndrome. It is a genuinely contested condition, not currently a widely recognised diagnosis in mainstream medicine, and it sits outside routine NHS practice. Here is a balanced view.

The idea, first described by Dr Ritchie Shoemaker, is that some genetically susceptible people cannot clear biotoxins from water-damaged buildings well, leading to ongoing immune activation and wide-ranging symptoms. A 2024 review of CIRS treatment found a modest set of published studies, including a couple of controlled trials [16]. Supporters argue the immune changes are measurable and real. Critics point out that CIRS lacks agreed, standardised criteria — three different case definitions have been put forward since 2006 — and that the supporting research base is narrow, with the large majority of published treatment studies coming from a single research group [16].

Water-damaged buildings can clearly affect health, especially the airways and immune system. Whether the full CIRS framework is the right way to explain complex illness is still being debated. Be curious about it; do not treat it as a settled, universal answer.

How do I know if mould is really the problem?

The honest answer is that you often cannot tell from symptoms alone — because the overlap with other conditions is enormous. That is exactly why self-diagnosis so often goes wrong, and why testing matters.

Two things move you from guessing to seeing. First, a clear history: have you lived or worked somewhere with damp, leaks, flooding or visible mould — and did your symptoms track with time spent there? (See the FAQs below for how to check your building, if you’re not sure.) Second, structured testing that shows what is actually happening in your gut, rather than assuming one cause. Healthpath’s Ultimate Gut Health Test uses an advanced stool test to look at microbiome balance, gut function and inflammation, with a qualified practitioner reviewing your results alongside your symptoms and giving you a personalised plan and recorded video.

Where does a urine mycotoxin test fit in?

If you have a genuine water-damaged-building history and gut symptoms that have not budged despite thorough treatment, a urine mycotoxin test can be a useful next piece of the picture. But it only helps if you understand exactly what it does and does not do — so let me be straight with you.

What it measures. A urine mycotoxin test looks at mycotoxins your body is excreting — a window onto your recent exposure and body burden.

What it cannot do on its own. It cannot diagnose mould-related illness, and it cannot tell you whether a mycotoxin came from your building or your breakfast. Because low-level food exposure is so common, mycotoxins show up in the urine of healthy people too. This is a real limitation, and anyone who tells you a positive result alone “proves” mould illness is overstating the science.

How to make the result more meaningful. Two things turn this from a number into useful information. The first is preparation: following a low-mould diet — cutting back on things like aged cheese, dried fruit, alcohol, peanuts and coffee — for around three days before testing helps reduce the dietary-intake confounder, so the result better reflects retained and environmental exposure rather than last night’s dinner. The second — and this is the part that matters most — is interpretation: the result is only worth having when a qualified practitioner reads it alongside your full history, your environment and your symptoms (and possibly your gut test results). A result without context is easy to misread in either direction.

That is the model Healthpath is built around, and it is why the practitioner interpretation and review is not an optional extra, it is the part that makes the test worth doing.

Here is a simple way to weigh up the two most relevant options.

For many people the sensible order is to assess the gut directly first (SIBO Test or Ultimate Gut Health Test), and to bring in mycotoxin testing where the history and the stalled progress point that way. A practitioner can help you decide the order.

What can I do if I suspect mould is affecting my gut?

If you suspect mould could be playing a role, five things are worth doing. None is a quick fix, and none is guaranteed — but all are reasonable ways to reduce your load and support your gut while you investigate:

1. Reduce ongoing exposure where you can. The WHO is clear that the single most useful action for damp buildings is to prevent and reduce the moisture that lets mould grow [1] — fixing leaks, improving ventilation, drying damp areas. If a building has a serious, ongoing water problem, addressing the source matters more than any supplement.
2. Support your gut barrier through diet. A varied, fibre-rich, whole-food diet feeds a diverse microbiome and supports the gut lining. Polyphenol-rich plants, fermented foods and a wide range of vegetables all help the gut cope with everyday challenges [8].
3. Look after the basics. Sleep, stress and movement all shape gut function and immune resilience. Not glamorous, but they change how well your gut copes.
4. Get an accurate picture before acting on assumptions. Testing and a practitioner review help you avoid spending months chasing the wrong cause — and avoid unnecessary restriction, which can make gut symptoms worse over time.
5. Work with a qualified professional. Mould-related illness sits at the edge of current evidence — exactly where personalised, expert support is worth more than internet protocols. A good practitioner will hold the uncertainty honestly and weigh mould against the many other possible causes.

None of the above is intended to treat or cure any condition. It is a way to support your body and gather better information.

Frequently asked questions

I’ve had gut issues for years and tried everything — could a building really be the missing piece? It is worth asking. Where a stubborn gut picture has resisted thorough treatment and there is a history of damp or water damage, mould exposure is a reasonable factor to investigate. It is rarely the whole story, but it is one that is easy to miss because most gut advice only looks at food.

Can mould definitely cause gut problems? Not in the clear-cut way many online claims suggest. Cell and animal studies show mycotoxins can damage the gut lining and shift the microbiome, and experienced clinicians see a recurring association with water-damaged buildings. But human evidence at everyday exposure is still limited, so it is fairer to say mould may contribute in some people than that it definitely causes gut problems.

Is a urine mycotoxin test enough to diagnose the cause of my symptoms? No — not on its own. Exposure is common, and a positive result does not equal a diagnosis or tell you the source. Its value comes from proper preparation and from a practitioner interpreting it alongside your history and other testing.

I have bloating. Should I assume it is mould? No. Bloating has many common causes, including SIBO, food intolerance and constipation. Mould is one possibility, and often not the most likely one. Testing helps you find the real driver.

How can I tell if my home or workplace actually has a mould problem? Look for musty smells, condensation on windows, watermarks or discolouration on walls or ceilings, and any history of leaks, flooding or subsidence — mould can also grow unseen inside walls or under flooring, so appearance alone isn’t reliable. If you’re unsure, a professional damp survey or an indoor air-quality/mould test can confirm what’s actually there, rather than relying on smell or guesswork.

What is the first sensible step if I’m worried? Reduce any obvious damp or mouldy exposure at home, and consider a structured gut assessment so you can see what is actually happening. If you have a clear water-damaged-building history and stalled gut progress, that is the picture where mycotoxin testing, done properly, earns its place.

A note on getting support

If your symptoms are severe, persistent or worrying, please speak to your GP — especially for unexplained weight loss, blood in the stool, difficulty swallowing, or symptoms that wake you at night. These need proper medical assessment, and mould theories should never delay that.

For ongoing gut symptoms that have not settled, a functional medicine approach can add value by looking for root contributors and building a personalised plan. Mould may be one piece of that picture. It is rarely the whole picture, and it should be weighed carefully alongside everything else.

Scientific references

1. World Health Organization. WHO Guidelines for Indoor Air Quality: Dampness and Mould. 2009.
2. European Food Safety Authority. Deoxynivalenol in food and feed: occurrence and exposure. EFSA Journal. 2013.
3. Carballo D, et al. Assessment of Human Exposure to Deoxynivalenol, Ochratoxin A, Zearalenone and Their Metabolites Biomarker in Urine Samples. Toxins. 2021.
4. World Health Organization. Health effects associated with dampness and mould (WHO Guidelines for Indoor Air Quality, NCBI Bookshelf).
5. Robert H, et al. Impact of mycotoxins on the intestine: are mucus and microbiota new targets? J Toxicol Environ Health B. 2017.
6. Gonzalez-Arias CA, et al. Effects of Mycotoxins on the Intestine. Toxins. 2019.
7. Huo W, et al. Mycotoxins and the Intestinal Epithelium: From Barrier Injury to Stem Cell Dysfunction. Toxins. 2025. https://pubmed.ncbi.nlm.nih.gov/41295849/
8. Intestinal barrier permeability: the influence of gut microbiota, nutrition, and exercise. 2024.
9. Więckowska M, et al. Gut as a Target of Ochratoxin A: Toxicological Insights and the Role of Microbiota. Int J Mol Sci. 2025.
10. Mafe AN, Büsselberg D. Microbiome–Mycotoxin Interactions and Probiotic Strategies: Implications for Gut Health and Cancer. Front Nutr. 2026.
11. Sorathia SJ, et al. Small Intestinal Bacterial Overgrowth. StatPearls. 2020.
12. Ghoshal UC, et al. Asian-Pacific consensus on small intestinal bacterial overgrowth in gastrointestinal disorders. 2022.
13. Maresca M, et al. The mycotoxin deoxynivalenol affects nutrient absorption in human intestinal epithelial cells. J Nutr. 2002.
14. Tang X, et al. The inflammatory injury of porcine small intestinal epithelial cells induced by deoxynivalenol is related to the decrease in glucose transport. J Anim Sci. 2024.
15. Brewer JH, Thrasher JD, Straus DC, Madison RA, Hooper D. Detection of Mycotoxins in Patients with Chronic Fatigue Syndrome. Toxins. 2013.
16. Dooley M, Vukelic A, Jim L. Chronic inflammatory response syndrome: a review of the evidence of clinical efficacy of treatment. Ann Med Surg. 2024.

This article is for educational purposes only. It is not intended to diagnose, treat, cure or prevent any disease. Always speak to a qualified healthcare professional before making changes to your health regime.