Mould and Mycotoxins: What the Evidence Shows

Mould is an everyday organism with a surprisingly contentious place in health. Everyone agrees that damp, mouldy homes are unhealthy, and in several countries deaths linked to mould in poor quality housing have prompted public inquiries and new regulations. At the same time, a growing number of patients are told that mould toxicity explains fatigue, cognitive problems, pain and many other symptoms, on the basis of urine tests and questionnaires, and are prescribed lengthy treatment protocols. Separating these 2 narratives is essential.

Moulds and mycotoxins

Moulds are fungi that grow on damp organic materials. Indoors, they flourish where moisture persists: leaks, condensation, poor ventilation and flooding. They release spores and fragments into the air, along with volatile organic compounds that produce a musty smell. Some moulds produce mycotoxins, toxic secondary metabolites. Mycotoxin exposure is well established as a food safety issue; its importance through indoor air exposure is much less clear.

What is well established

Respiratory and allergic effects

Major reviews by the World Health Organization and the United States Institute of Medicine concluded that there is sufficient evidence of an association between damp or mouldy indoor environments and upper respiratory symptoms, cough, wheeze and asthma symptoms in people with asthma. Later evidence supports an association with the development of asthma, particularly in children. People with allergies to mould, and children, older adults and people with chronic respiratory disease are particularly vulnerable.

Specific mould related diseases

Dietary mycotoxins

Aflatoxins, produced by moulds on poorly stored crops such as maize and groundnuts, are classified as carcinogenic to humans and are a major cause of liver cancer in parts of Africa and Asia, particularly in combination with hepatitis B. Other food mycotoxins, such as ochratoxin and fumonisins, are regulated in many countries. Food safety measures and proper storage reduce exposure.

What is contested

The “toxic black mould” story

In the 1990s, a cluster of infants with pulmonary haemorrhage in Cleveland was linked to Stachybotrys chartarum, a mould associated with water damaged buildings. The association attracted extensive publicity. A subsequent review by the United States Centers for Disease Control and Prevention found shortcomings in the original investigation and concluded that the association had not been proven. The phrase “toxic black mould” persists in popular culture despite this.

Mould toxicity and chronic inflammatory response syndrome

Some practitioners describe a systemic illness caused by indoor mould exposure, sometimes called chronic inflammatory response syndrome or mould toxicity, characterised by fatigue, cognitive difficulties, pain, gut symptoms and many other features. Diagnosis often relies on symptom questionnaires, visual contrast tests, panels of immune markers and urine mycotoxin testing, followed by treatment with binding agents, antifungals and extended protocols.

These diagnostic approaches have not been validated. Urine mycotoxin tests detect mycotoxins in most people, because mycotoxins are common in the food supply, and they have not been shown to distinguish people with building related illness from others. Allergy and immunology organisations have concluded that there is insufficient evidence that inhaled mycotoxins in typical indoor environments cause systemic illness. The proposed syndrome has not been independently confirmed in controlled studies.

Patients who receive this diagnosis often have genuine and distressing symptoms, and some live in genuinely damp homes. The appropriate response is to take the symptoms seriously, address any real damp problem, assess for established conditions and other causes, and avoid unvalidated tests and lengthy treatments without evidence.

Assessing a patient concerned about mould

1. Take an environmental history: visible mould, musty smell, leaks, flooding, condensation, ventilation, and whether symptoms improve away from the building.
2. Assess for established conditions: asthma, allergic rhinitis, sinusitis, hypersensitivity pneumonitis, and in immunocompromised patients, fungal infection.
3. Consider allergy testing for moulds where allergic disease is suspected, interpreted with the history.
4. Investigate other causes of fatigue, cognitive and other systemic symptoms, such as anaemia, thyroid disease, sleep disorders, depression and medicines.
5. Avoid urine mycotoxin testing and other unvalidated tests.

Fixing the building

The most effective intervention for mould related health problems is controlling moisture.

• Repair leaks and water damage promptly.
• Keep indoor humidity below about 50 to 60 percent.
• Ventilate kitchens, bathrooms and laundry areas.
• Dry water damaged materials within a day or 2 where possible.
• Clean small areas of mould on hard surfaces; remove porous materials that are extensively affected.
• Seek professional remediation for large areas, and protect vulnerable people during remediation.
• For tenants, support may be needed to ensure landlords address damp, which in some countries is a legal responsibility.

Air testing for mould spores is rarely necessary when visible mould or damp is present; the priority is to find and fix the moisture source.

An illustrative case

A family living in a rented flat with persistent condensation and black mould around the windows reports that their 7 year old has frequent wheeze and night cough, and the mother has nasal congestion and fatigue. The child is assessed and diagnosed with asthma; mould allergy testing is positive. The practitioner supports the family in documenting the damp and requesting repairs from the landlord, and advises on ventilation and humidity control meanwhile. The mother’s fatigue is investigated separately; her ferritin is low, and iron treatment helps. After repairs and asthma treatment, the child’s symptoms improve substantially. The mould was a real problem with a real solution, and the fatigue had a separate, treatable cause.

Real damp, real harm, careful claims

Damp and mouldy homes cause genuine respiratory and allergic harm, particularly for children and vulnerable people, and fixing them is a public health priority. Broader claims of systemic mould toxicity diagnosed by unvalidated tests lack evidence. Practitioners can help most by addressing the real problems and investigating symptoms thoroughly.