Fungi, Mould and the Gut: Why This Connection Deserves More Attention

For years, conversations about health have tended to focus on bacteria. We hear about the microbiome, probiotics, fermented foods and the importance of maintaining a healthy balance of beneficial bacteria in the gut.

But there is another part of this internal ecosystem that deserves more attention: fungi.

Our bodies are home to a complex community of microorganisms, including bacteria, viruses and fungi. The fungal component of the gut microbiome is often referred to as the mycobiome. Although fungi make up a relatively small proportion of the gut microbial community, research suggests that they can have a significant relationship with our immune system and the wider microbial ecosystem.

And this is where the conversation around fungal health, mould and the gut becomes particularly interesting.

We are surrounded by fungi

Fungi are everywhere. They exist naturally in our environment, in soil, food, plants, buildings and the air around us. Exposure to fungal spores is therefore a normal part of everyday life.

The problem is not simply that fungi exist. The question is what type of exposure are we experiencing, how much, for how long, and how is our individual body responding?

Mould thrives in damp environments. Leaks, condensation, flooding and persistent moisture can create conditions where mould grows indoors.

The World Health Organization has recognised dampness and mould as an important indoor environmental health issue. Its review found associations between damp or mouldy buildings and respiratory symptoms, allergies and asthma, as well as effects on immune responses.

The CDC similarly notes that exposure to damp and mouldy environments can cause symptoms such as stuffy nose, sore throat, coughing, wheezing, irritated eyes and skin reactions. People with asthma or mould allergies can experience more significant reactions, while people with severely weakened immune systems can be vulnerable to certain fungal infections.

So there is no question that mould can matter for health.

But there is another question worth asking:

Could our internal fungal ecosystem matter too?

The forgotten part of the microbiome

When we talk about the microbiome, bacteria usually take centre stage.

However, research into the gut mycobiome is beginning to reveal a much more complex picture.

Fungi such as Candida, Saccharomyces and other organisms can be found in the gastrointestinal tract. They interact with bacteria, the intestinal environment and our immune system. Researchers are investigating how changes in this fungal community — sometimes described as fungal dysbiosis — may relate to different aspects of health and disease.

This doesn't mean that having fungi in the gut is automatically a bad thing.

In fact, some fungi are normal members of the microbial community.

The body is constantly managing relationships between microorganisms and the immune system. The balance between these organisms may be more important than simply trying to help reduce every fungus.

That is an important distinction.

The goal isn't necessarily to live in a completely “fungus-free” body. It is about understanding the ecosystem and what helps maintain a healthy balance.

The gut and immune system are closely connected

One of the most fascinating areas of research is the relationship between the gut microbiome and immune function.

The intestinal tract isn't simply a digestive tube. It is a major interface between the outside world and the body's internal environment, containing a substantial proportion of our immune system.

Research suggests that interactions between gut fungi, bacteria and immune cells can influence immune responses. Scientists are also investigating connections between the gut mycobiome and conditions affecting other parts of the body.

For example, researchers are exploring the gut–lung axis — the idea that changes within the gut microbial ecosystem can influence immune activity in the respiratory system.

A 2024 review examined the gut mycobiome in relation to asthma and described evidence linking changes in intestinal fungal communities with respiratory immune responses. Importantly, much of this field is still developing, and researchers continue to investigate exactly how these relationships work.

This is where things become genuinely exciting.

Rather than thinking about our health as a collection of separate organs, we can begin to appreciate the body as an interconnected ecosystem.

What about mould exposure and the gut?

This is where we need to be careful.

It is tempting to make a direct leap from:

“Mould can affect health” → “Mould causes gut fungal overgrowth.”

The evidence does not currently justify such a simple conclusion.

Mould exposure is well recognised as a potential cause of respiratory and allergic problems, particularly in damp buildings. However, claims that ordinary household mould exposure inevitably causes a systemic fungal infection or “mould growing throughout the body” are not supported by the evidence.

Likewise, finding fungi such as Candida in the gut does not automatically mean someone has a fungal infection.

There is a big difference between colonisation, microbial balance and invasive infection.

This distinction matters because health information should empower people without creating unnecessary fear.

So why pay attention to the gut?

Because the gut is an ecosystem.

Diet, medications, illness, lifestyle and many other factors can influence the microorganisms living within it. Research suggests that antimicrobial exposure, diet and age can all influence the composition of the gut mycobiome.

Rather than focusing on one organism or looking for a single explanation for every symptom, it may be more useful to consider the bigger picture.

How are we supporting our gut environment?

How diverse is our diet?

Are we getting enough fibre and plant-based foods?

Are we unnecessarily disrupting our microbiome?

Are we paying attention to our living environment?

And, importantly, are we addressing obvious dampness or mould problems in our homes and workplaces?

These are practical questions that can form part of a broader approach to health.

Looking at the bigger picture

The renewed public conversation around fungal diseases and mould provides an opportunity to ask better questions.

We know that damp and mouldy environments can affect health, particularly respiratory health. We also know that fungi are a natural and important part of the human microbial ecosystem.

What we are still learning is exactly how these different fungal environments — inside and outside the body — interact with our immune system and wider health.

The science is evolving.

And perhaps that is precisely why this subject deserves more attention.

Rather than being frightened by fungi, we can become more informed about them.

Rather than focusing solely on helping reduce microorganisms, we can begin to understand the importance of balance, resilience and the ecosystems that support our health.

The gut–fungus connection is still an emerging field, but it could change the way we think about the relationship between our environment, our microbiome and our overall wellbeing.

Sometimes the most interesting health questions aren't about one particular symptom or one particular organism.

They're about how everything connects.

If you'd like to explore ways of supporting your gut health and overall wellbeing, click the link to find out more.

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