Mould and Mycotoxins
Mould toxins, trichothecenes, ochratoxin
What is it?
Mould grows wherever moisture exceeds approximately 60% relative humidity for a sustained period. In buildings, this means bathrooms, basements, behind walls with water damage, in HVAC systems, and anywhere with poor ventilation. Moulds produce mycotoxins as secondary metabolites, some of which are acutely toxic. The most commonly encountered indoor moulds are Aspergillus, Penicillium, Cladosporium, and Stachybotrys chartarum (so-called black mould). Older housing stock with poor insulation, flat roofs, or histories of water damage is disproportionately affected. Significant mould growth often occurs in hidden spaces, and occupants may be symptomatic for months before a source is identified.
What it does to your body
Respiratory damage
Mould spore inhalation causes asthma, hypersensitivity pneumonitis and chronic sinusitis. The respiratory immune reaction can persist after exposure ceases.
Neurological effects
Stachybotrys mycotoxins (trichothecenes) have neurotoxic properties. Chronic mould exposure has been linked to brain fog, memory impairment and mood disorders in case studies and prospective research.
Immune disruption
Mycotoxins interfere with immune function, acting as immunosuppressants at low doses and causing hyperreactive responses at higher doses.
Chronic fatigue
Chronic mould exposure is associated with conditions presenting as chronic fatigue in case studies, though establishing causation in individuals is challenging.
Liver and kidney toxicity
Aflatoxin is a potent liver carcinogen. Ochratoxin, found in water-damaged buildings and contaminated food, is nephrotoxic at elevated exposures.
How widespread is the problem?
The WHO estimates that 10 to 50% of indoor environments in Europe, North America, Australia and India have significant water damage and mould problems. In the UK, approximately 25% of homes have been assessed as having a damp or mould problem. Children, elderly people and those with compromised immune systems are most affected.
Where it hides in your home
Key research
WHO Guidelines for Indoor Air Quality: Dampness and Mould
WHO review finding sufficient evidence that mould exposure increases risk of respiratory symptoms, asthma development, and hypersensitivity pneumonitis.
Fisk et al. Association of Dampness and Mould with Respiratory Outcomes
Meta-analysis of 33 studies: significant associations between building dampness and mould with upper and lower respiratory symptoms, asthma development and exacerbation.
CDC Mould and Your Health Overview
CDC documentation of mould health effects, noting that all moulds should be treated as a health hazard and that damp materials should be remediated regardless of mould type.
Mycotoxin effects typically improve after removing the mould source and reducing exposure, though neurological effects can persist. Some people have genetic variants that make mycotoxin clearance slower, explaining why the same home affects household members differently.