How Mould Makes You Sick

How Mould Makes You Sick

Mould can make you sick due to inflammation, oxidative stress, toxicity, infection, allergy, and irritant effects of exposure.

Responses to mould exposure will vary from person to person based on our genetics, the duration and severity of exposure, and our overall health status. 

Many factors will influence our overall health, including our gut microbiome, nutrient status, physical activity levels, relationships, immune system, and toxic burden. 

The research into sick building syndrome (i.e., getting ill from exposure to damp/water-damaged environments) has consistently demonstrated that overall exposure is the main factor associated with getting sick from mould. (source)

It’s Not Just Mould

It’s important to note that illness from water-damaged buildings results from a combination of factors present in indoor environments, including mould spores and fragments, mycotoxins, bacteria, bacterial endotoxins, and cell wall components, as well as other factors.

Let’s summarise the main ones quickly.

Bacteria And Endotoxins Cause Symptoms Too

Research has demonstrated that bacteria are often present in water-damaged buildings. One way of classifying bacteria is as gram-positive and gram-negative bacteria. Gram-positive bacteria are often associated with causing pulmonary (airway) diseases. Gram-negative bacteria, such as Pseudomonas, have been shown to cause illness through infections and the effects of endotoxins (more on endotoxins below). 

The extent to which an individual will be affected by exposure to bacteria and endotoxins will depend on the duration and severity of exposure and their immune system function (which will be influenced by everything from genetics to their gut microbiome and nutrient status).

Endotoxins, for example, lipopolysaccharides that are found in the cell walls of bacteria, are known to trigger a profound inflammatory response, especially when leaky gut is present. I have discussed this in more detail on my blog on die off symptoms from SIBO. To make matters worse, studies have shown that endotoxins act synergistically with mycotoxins and exacerbate the inflammatory response.

A lot of the research on endotoxins, in the context of water-damaged buildings, comes from flood-damaged homes in New Orleans. One study that evaluated homes affected by hurricanes Katrina and Rita showed that it wasn’t just high levels of mould spores that were causing adverse health effects; endotoxins were also detected at high levels known to cause health issues.

I wanted to highlight this as it is easy to run a mycotoxin test, have a positive result, and focus just on mycotoxins when, in reality, there may be other things contributing to symptoms. (source)

How Mould Makes You Sick: Typical Symptoms

There is broad agreement in the medical world that respiratory symptoms are common after exposure to a water-damaged indoor environment. However, a typical patient often presents with multiple symptoms in multiple bodily systems, which are often debilitating. These individuals might be suffering from chronic inflammatory response syndrome.

Symptoms may include fatigue, neurocognitive symptoms, myalgia, arthralgia, headache, insomnia, dizziness, anxiety, depression, irritability, gut problems such as diarrhoea, tremors, balance disturbance, palpitations, vasculitis, angioedema, and autonomic nervous system dysfunction. (source)

The development of new-onset chemical sensitivity is also commonly seen after exposure and can severely impact a person’s life.

Typical Conditions Caused By Mould

Types of disorders that can be seen resulting from water-damaged environments (and this exposure to mould, mycotoxins, and bacteria) include: fungal or/and bacterial infections, chronic and fungal rhinosinusitis, allergies, respiratory conditions such as asthma, other hypersensitivity reactions, pulmonary inflammatory disease, immune suppression and modulation, autoimmune disorders, mitochondrial toxicity, various cancers, kidney disease, liver disease, and neurotoxicity. (source)

Mechanisms Behind The Symptoms

Various mechanisms, including infection, toxicity, allergy, inflammation, and oxidative stress, can cause illness caused by living in a water-damaged building. 

It’s important to appreciate that many of these mechanisms listed above interact in an individual at any given time, making it imperative to address the illness with a comprehensive, multifaceted approach.

Let’s take a look at each mechanism.

Oxidative Stress

One of the leading causes of injury is oxidative stress. 

This is an important concept as it helps direct the approach to treatment, which needs to:

  1. Focus on removing ongoing sources of oxidative stress in the body, such as mycotoxins.
  2. Starting treatments such as antioxidants to reduce oxidative stress – e.g., liposomal glutathione, NAC, zinc, among others. 

Oxidative stress is a well-understood, significant mechanism behind mould sickness. For example, ochratoxin A, which I frequently find to be elevated in clients’ test results, is a known cause of cellular changes associated with oxidative stress. 

A recent study showed that when exposed to ochratoxin A, human mononuclear cells showed increased levels of 8-OhdG, a marker of oxidative stress and one we often test in urine. An important finding from this study was that the addition of NAC, a building block for glutathione (a master antioxidant in the human body), was able to significantly block some of the adverse effects of ochratoxin A on the human cells being studied. (source)

Inflammation & Autoimmunity

Inflammation triggered by exposure also appears to play a significant role in illness during and after exposure to water-damaged environments.

Multiple Sclerosis: A correlation between fungal infection and Multiple Sclerosis has been described for Candida. Also, another study found that neural protein autoantibodies were increased in several individuals exposed to mould. In yet another study, gliotoxin exposure worsened the expression of an experimental autoimmune encephalomyelitis (EAE) model by triggering neuroinflammation and demyelination. (source)

Rheumatoid Arthritis: A case study published in the 80s, which admittedly only had a very small number of patients in, described a stronger sensitisation to Aspergillus antigens in rheumatoid arthritis patients compared to healthy participants. While there is very limited human research at this time, there is an experimental rheumatoid arthritis study that looked at two mycotoxins, ochratoxin A and Deoxynivalenol, that showed that both mycotoxins have the potential to increase the susceptibility and severity of rheumatoid arthritis. (source)

Inflammatory Bowel Disease: Research has shown that two mycotoxins, Deoxynivalenol and Zearalenone, have the potential to induce the onset of colitis, showing increased inflammation in the large intestine. Other research in rats has shown that mycotoxins worsen colitis symptoms. (source)

Allergy and Non Allergic Respiratory Disease

Respiratory illnesses are well known, even in conventional medicine, to be associated with mould exposure. Examples include chronic rhinosinusitis, allergic rhinitis (including allergic fungal rhinitis), sinusitis, asthma, and conjunctivitis. (source)

“It has been estimated that 21% of asthma in the United States is attributable to dampness and mould exposure.” (source)

On top of this, exposure to mould odours at home more than doubles the risk of developing asthma in children, and exposure to workplace mould more than quadruples the risk of new-onset asthma!

Interestingly, studies have found that allergies in response to mould are often not IgE-mediated. For example, in one study, only 33% of the probable occupational asthma patients were atopic to any environmental antigen, and only 20% were sensitized to mould allergens. This suggests that it was not a type 1 allergy causing symptoms but a different mechanism. (source)

Infection and Colonisation

Fungal infections are common in the sinuses and the gut and can be the result of exposure to mould in water-damaged properties. For many years, it was thought this could only be associated with people with suppressed immune systems, but this has also been seen in immunocompetent people. Direct exposure to elevated levels of mould spores indoors can contribute to fungal disease, either directly by allowing seeding for fungal growth, such as that occurring in nasal mucosa, or by direct toxic effects and immune system alteration resulting from exposure. 

Another key thing to understand is that some treatments, such as antibiotics and steroids, can contribute to fungal growth throughout the body, including in nasal, sinus, and gastrointestinal tissue. (source)

Nasal Infections

Nasal infections and colonization deserve their own discussion as many people develop respiratory symptoms during and after exposure to mould, but you don’t need symptoms to have mould colonization in your sinuses. 

“Untreated nasal and sinus infections can be a cause of ongoing symptoms and should be addressed. “(source)

Allergic fungal rhinitis is known as a cause of persistent nasal infection. A Mayo Clinic study found fungal growth in an amazing 96% of patients with chronic sinusitis!

In those patients, the types of moulds identified included Aspergillus, Penicillium, and Fusarium, as well as many other types of mould that are capable of producing mycotoxins.

What this means is if we have been colonized by mould and leave the property, we become our own mobile mouldy property!

Treatment includes the avoidance of exposure to elevated mould spore counts, either through remediation, leaving the property, or the use of air purifiers, as well as sinus irrigation, and nasal antifungals and antimicrobials which can include agents such as xylitol that may help break down any biofilms present.

Gut Infections & Imbalances 

There is increasing evidence that mould and mycotoxins cause damage to the gut, and, as I have already said, conventional treatments often prescribed to treat illness, such as antibiotics and steroids, can cause significant changes in the gut microbiome (including increased fungal colonization), which may even result in reduced metabolism of mycotoxins (and other toxins!). 

Identifying and treating these imbalances is a key part of successful recovery from mould illness. This is where a comprehensive gut microbiome test can be so helpful. The use of both bacterial and yeast probiotics, treating infections with natural antimicrobial agents such as oregano oil, and identifying and avoiding food allergens, intolerances, and sensitivities can all be incredibly helpful here. (source)

How Does Mould Get in The Body

We eat them, breathe them in, and they can even penetrate our skin. 

While exposure to mycotoxins in our food has been discussed extensively in the literature, you may be surprised to know that there is substantial information about airborne and transdermal routes of exposure. 

Airborne exposure is likely the most significant route of exposure in water-damaged indoor environments.

The airborne presence of mycotoxins has been well documented in research studies and has been reported to cause human illness throughout the medical literature. 

Some mycotoxins can also penetrate through the skin, and our skin could come in to contact with mycotoxins via mycotoxin-contaminated items (pillowcases, bed linen, clothes, etc). This exposure, therefore, even has the potential to occur after a person has left the mouldy property since many people bring mould and mycotoxin-contaminated belongings to their new home. 

One study showed that aflatoxin B1, ochratoxin A, citrinin, and zearalenone all penetrated human skin in vitro and that ochratoxin had the highest permeability. (source)


Various mechanisms, including infection, toxicity, allergy, inflammation, and oxidative stress, can cause illness caused by mould. It is for this reason that a comprehensive and holistic approach is essential to successful treatment. 

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