The Health Risks of Mould — What You Need to Know
Mould exposure causes serious respiratory and immune problems. Understanding the risk is the first step.
How Mould Affects Human Health
Mould produces microscopic spores that become airborne and are inhaled by occupants of affected properties. These spores can trigger a range of health effects — from mild allergic reactions to serious respiratory illness — depending on the species of mould, the concentration of spores, the duration of exposure and the health status of the individual exposed.
The NHS and World Health Organisation both recognise the health impacts of indoor mould as a significant public health issue. The WHO estimates that 10–50% of indoor environments in Europe, North America and other developed regions have clinically significant dampness and mould problems — and that the resulting health impacts are substantial.
In 2020, two-year-old Awaab Ishak died in his social housing home in Rochdale from a severe respiratory condition directly caused by exposure to black mould. The coroner’s conclusion led directly to the introduction of Awaab’s Law, making rapid remediation of damp and mould a legal obligation for social housing providers.
Health Conditions Linked to Mould Exposure
Asthma & Respiratory Disease
Mould spores are a well-established trigger for asthma attacks. Long-term exposure to indoor mould is associated with the development of asthma in children who did not previously have it, and the worsening of asthma in people with pre-existing conditions.
Allergic Rhinitis
Mould allergy causes persistent nasal congestion, sneezing, runny nose and itchy eyes — symptoms often misattributed to hay fever or pet allergies. Mould allergy affects people year-round, not just in pollen season.
Skin Conditions
Mould spore exposure can trigger urticaria (hives) and eczema flares, particularly in children and individuals with existing skin sensitivities.
Neurological Symptoms
Mycotoxins produced by black mould (Stachybotrys) have been associated with headaches, brain fog, difficulty concentrating and fatigue — sometimes described as ‘sick building syndrome’.
Fungal Infections
In immunocompromised individuals, inhaled mould spores can cause serious fungal infections including aspergillosis — a potentially life-threatening condition in people with compromised immune systems.
Child Development
Children living in damp and mouldy homes have higher rates of respiratory infections, absence from school and developmental impacts. Early childhood mould exposure is a risk factor for lifelong respiratory disease.
Which Moulds Are Most Harmful?
While all indoor mould should be treated seriously, some species present a greater health risk than others:
- ✓Stachybotrys chartarum (black mould) — the most hazardous indoor mould. Produces trichothecene mycotoxins. Requires very wet conditions to grow and is typically found behind walls and ceilings with persistent water damage.
- ✓Aspergillus — a diverse genus with some species producing aflatoxins and others causing aspergillosis in immunocompromised individuals. Common on building materials and organic debris.
- ✓Penicillium — produces mycotoxins including ochratoxin A. Common in damp buildings and a significant allergen. Often appears as blue or green surface mould.
- ✓Cladosporium — one of the most common indoor moulds. A significant allergen and asthma trigger, particularly in those with respiratory sensitisation.
Protecting Your Family
The most effective way to protect your family from mould-related health problems is to eliminate the moisture source that is enabling mould growth. This requires professional diagnosis to identify the true cause — condensation, rising damp, penetrating damp or a plumbing leak — and targeted treatment.
In the meantime, the following measures reduce exposure while the underlying cause is addressed:
- ✓Improve ventilation — open windows, use extractor fans in kitchens and bathrooms
- ✓Reduce indoor humidity — avoid drying washing on radiators, use a dehumidifier if necessary
- ✓Clean surface mould with appropriate biocidal products while wearing a mask and gloves
- ✓Do not sleep in severely affected rooms, particularly for children and vulnerable individuals
- ✓Report damp and mould to your landlord in writing if you are a tenant — Awaab’s Law may require them to act within 14 days
How do I know if mould is making me ill?
If you notice that symptoms (cough, runny nose, headaches, fatigue) improve when you are away from the property and worsen when you return, indoor air quality — including mould — may be a factor. A professional mould inspection is recommended.
Is a small amount of mould dangerous?
Any visible mould indicates a moisture problem that needs addressing. Small areas of surface mould on non-porous surfaces in bathrooms can be cleaned. Mould on walls, behind furniture or in rooms other than bathrooms and kitchens should be investigated professionally.
Should I leave the property if mould is severe?
If mould is extensive — covering more than 1 square metre or present in multiple rooms — and if occupants are experiencing health symptoms, particularly if children, elderly or immunocompromised individuals are present, professional advice should be sought. In severe cases, temporary relocation may be appropriate.
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