Beyond the Lungs: Is There Scientific Evidence Linking Damp and Mould to Multi-System Illness?

For decades, damp and mould have largely been viewed as a respiratory problem. Asthma, allergies, coughing and wheezing are well-established consequences of living in a damp building. But increasing numbers of clinicians, researchers and patients are asking a much bigger question.

Can exposure to damp and mould contribute to illness throughout the body, not just the lungs?

The short answer is yes. There is growing scientific evidence that it can. However, it is important to distinguish between what is already accepted by the international scientific community and where research is still developing.

Understanding this distinction is essential for healthcare professionals, housing providers and anyone seeking evidence-based guidance.

What is already established?

The strongest evidence comes from the World Health Organization (WHO).

Its landmark publication, WHO Guidelines for Indoor Air Quality: Dampness and Mould, concludes that damp indoor environments are consistently associated with:

• Increased asthma
• Asthma exacerbations
• Respiratory symptoms
• Allergic symptoms
• Respiratory infections
• Disturbances of the immune system

Importantly, the WHO explains that occupants of damp buildings are exposed to far more than visible mould. Water-damaged buildings contain a complex mixture of:

• Fungal spores
• Fungal fragments
• Bacteria
• Endotoxins
• Allergens
• Volatile organic compounds (VOCs)
• Microbial metabolites
• Other biologically active particles

This means exposure is not to a single organism, but to a complex biological aerosol capable of interacting with the immune system.

Why the lungs are not the end of the story

The lungs are one of the largest interfaces between the body and the outside environment.

Every day, we inhale approximately 10,000 litres of air. Anything suspended within that air, including fungal fragments, bacterial components and microbial toxins, has the potential to interact with the immune system.

Once immune pathways are activated, the consequences need not remain confined to the respiratory tract.

Inflammation is a whole-body process. Immune mediators released in response to inhaled contaminants circulate throughout the body and may influence multiple organ systems.

This provides a biologically plausible explanation for why some individuals report symptoms including:

• Fatigue
• Brain fog
• Headaches
• Cognitive difficulties
• Muscle and joint pain
• Dizziness
• Gastrointestinal symptoms
• Skin reactions
• Autonomic dysfunction

The question researchers continue to investigate is how often this occurs, who is most susceptible, and what biological mechanisms are responsible.

Human evidence for systemic inflammation

One of the strongest human studies comes from Mustonen et al. (2016).

Researchers found that children living in homes with moisture damage demonstrated increased markers of systemic inflammation and altered cytokine responses.

This is particularly important because it demonstrates objective biological changes beyond the lungs, supporting the hypothesis that damp indoor environments may influence the immune system throughout the body.

What about fatigue?

Fatigue is one of the most frequently reported symptoms among people living in water-damaged buildings.

A 2025 systematic review by Dooley and McMahon examined the published literature between 2011 and 2018, representing more than 40,000 participants.

The review concluded that the available evidence supports an association between damp or mould exposure and fatigue.

However, the authors also acknowledged important limitations:

• Many studies were observational.
• Exposure assessment varied considerably.
• More prospective research is needed.

The review also contains declared conflicts of interest relating to expert witness work in Chronic Inflammatory Response Syndrome (CIRS), meaning its findings should be interpreted alongside independent evidence rather than in isolation.

Evidence from experimental research

Human studies are inevitably difficult because every building differs.

Controlled laboratory studies allow researchers to isolate exposure.

One particularly important study by Harding et al. (2020) exposed mice to inhaled mould spores and found:

• Activation of the innate immune system
• Neuroinflammation
• Behavioural changes
• Impaired cognitive performance

A later study by the same group (2023) demonstrated that even moulds not traditionally considered major mycotoxin producers were capable of producing inflammatory and neurological effects through inhalation.

Animal studies cannot prove identical effects occur in humans, but they provide important biological evidence showing that inhaled mould exposure can influence the brain and immune system.

How might this happen?

Researchers have identified several possible mechanisms.

These include:

• Chronic activation of innate immunity
• Cytokine dysregulation
• Oxidative stress
• Disruption of epithelial barriers
• Mast-cell activation
• Persistent inflammatory signalling

Reviews by Kraft et al. (2021) and Kritas et al. (2018) describe how fungal components and mycotoxins may interact with immune pathways capable of affecting multiple organ systems.

These mechanisms are biologically plausible, although much of the supporting evidence comes from laboratory studies, occupational exposure or foodborne mycotoxin research rather than typical residential environments.

What about Chronic Inflammatory Response Syndrome (CIRS)?

Perhaps the most debated area of mould research is Chronic Inflammatory Response Syndrome (CIRS).

Some clinicians believe exposure to water-damaged buildings can trigger a persistent multi-system inflammatory illness characterised by fatigue, cognitive dysfunction, pain and numerous neurological symptoms.

Several peer-reviewed papers, including studies of biomarkers, MRI brain imaging and treatment outcomes, support this possibility.

However, CIRS has not yet achieved universal acceptance within mainstream medicine.

Current limitations include:

• Relatively small study populations
• Limited independent replication
• Evolving diagnostic criteria
• Uncertainty regarding the specificity of proposed biomarkers

This does not mean CIRS has been disproven. Rather, it means further high-quality, independently replicated research is required before a definitive scientific consensus can be reached.

The historical perspective

Some critics still cite the 2004 Institute of Medicine (IOM) report as evidence that mould cannot cause systemic illness.

That is not what the report concluded.

The IOM found sufficient evidence linking damp buildings to several respiratory conditions but stated that evidence for fatigue, neurological disease and other systemic effects was insufficient, not absent.

Importantly, many of the mechanistic studies and epidemiological investigations discussed in this article were published after that review.

Science has continued to evolve.

Where does the evidence stand today?

The current evidence can be summarised as follows:

✔ There is strong international consensus that damp and mould-contaminated buildings adversely affect respiratory health.

✔ There is strong evidence that damp buildings can alter immune function and produce systemic inflammatory responses.

✔ There is growing evidence linking damp and mould exposure with fatigue, cognitive dysfunction and neurological symptoms.

✔ Experimental studies demonstrate biologically plausible mechanisms connecting inhaled microbial contaminants with whole-body inflammation.

✔ Whether these findings constitute a distinct chronic multi-system illness in susceptible individuals remains an active area of scientific investigation.

The take-home message

The debate should no longer be framed as whether mould is "just an allergy."

Modern research increasingly shows that water-damaged buildings expose occupants to a complex mixture of microbial particles capable of interacting with the immune system in ways that extend beyond the lungs.

While respiratory disease remains the most firmly established consequence of damp and mould exposure, the scientific literature increasingly supports the possibility that systemic inflammation, fatigue and neurological symptoms may also occur in susceptible individuals.

The lungs are the route of exposure, not necessarily the limit of disease.

As research continues to evolve, housing policy, clinical practice and building remediation should reflect the growing understanding that indoor environmental quality is fundamental to whole-body health.

References

1. World Health Organization. WHO Guidelines for Indoor Air Quality: Dampness and Mould. WHO Regional Office for Europe, 2009.

2. Mustonen K, et al. Moisture damage in home associates with systemic inflammation in children. Indoor Air. 2016.

3. Dooley DP, McMahon MA. Fatigue and exposure to mold and/or dampness: A systematic review of the literature from 2011–2018. Reviews on Environmental Health. 2025.

4. Harding CF, et al. Mold inhalation causes innate immune activation, neural, cognitive and emotional dysfunction. Brain, Behavior, and Immunity. 2020.

5. Harding CF, et al. Differential effects of exposure to toxic or nontoxic mold spores on brain inflammation and behaviour. Brain, Behavior, and Immunity. 2023.

6. Kraft K, et al. Mold, Mycotoxins and a Dysregulated Immune System. International Journal of Molecular Sciences. 2021.

7. Kritas SK, et al. Impact of mold on mast cell-cytokine immune response. Journal of Biological Regulators and Homeostatic Agents. 2018.

8. Institute of Medicine. Damp Indoor Spaces and Health. National Academies Press. 2004.