Is Mould Dangerous? Health Risks of Mould Exposure
Mould is more than an unsightly nuisance. For many Australians, it poses genuine health risks — from persistent allergies to serious respiratory illness. Here is what you need to know.
The short answer is yes — mould can be dangerous. The level of danger depends on the species of mould, the concentration of airborne spores, the duration of exposure, and your individual health status. While healthy adults may experience mild allergic symptoms, vulnerable groups including children, the elderly, and immunocompromised individuals face significantly greater risks.
According to the World Health Organization, occupants of damp or mouldy buildings have up to a 75% increased risk of respiratory symptoms and asthma. In Australia, where mould growth is prevalent due to our humid climate, understanding these risks is essential for protecting your household.
Types of Mould and Their Danger Levels
Not all mould is equally dangerous. The following species are the most commonly found indoors in Sydney homes and commercial buildings.
Stachybotrys chartarum (Black Mould)
Danger: HighOften called "toxic black mould," Stachybotrys produces mycotoxins that can cause serious respiratory issues, neurological symptoms, and immune suppression. It thrives on water-damaged cellulose materials (plasterboard, timber, paper) and appears as a dark greenish-black slimy growth. Professional removal with full containment is essential.
Aspergillus
Danger: Moderate to HighOne of the most common indoor moulds, Aspergillus includes over 180 species. Some produce aflatoxins — potent carcinogens. Aspergillus is particularly dangerous for immunocompromised individuals, potentially causing aspergillosis, a serious lung infection. It appears in various colours including green, yellow, white, and black.
Cladosporium
Danger: Low to ModerateA very common outdoor and indoor mould that appears olive-green to brown or black. While less toxic than Stachybotrys, Cladosporium is a significant allergen and can trigger asthma attacks, hay fever symptoms, and skin irritation. It commonly grows on fabrics, wood, and HVAC systems.
Penicillium
Danger: Low to ModerateBlue or green fuzzy mould often found on food, wallpaper, carpet, and insulation. Penicillium spreads rapidly and is a common cause of allergic reactions. Some species produce mycotoxins. While the genus famously gave us penicillin, indoor Penicillium growth should be addressed promptly.
Health Symptoms of Mould Exposure
Mould exposure can affect different body systems. Symptoms range from mild irritation to serious illness depending on the type of mould, level of exposure, and individual vulnerability.
Respiratory Symptoms
- •Persistent coughing or wheezing
- •Shortness of breath or difficulty breathing
- •Nasal congestion and sinus pressure
- •Throat irritation and hoarseness
- •Chest tightness
- •Worsening of existing asthma
Allergic Reactions
- •Sneezing and runny nose
- •Itchy, watery, or red eyes
- •Skin rashes or hives
- •Itchy skin or dermatitis
- •Post-nasal drip
Neurological Symptoms
- •Persistent headaches
- •Difficulty concentrating or "brain fog"
- •Memory problems
- •Dizziness or vertigo
- •Fatigue and lethargy
Immunocompromised Risks
- •Invasive fungal infections (aspergillosis)
- •Pneumonia or bronchitis
- •Chronic sinusitis
- •Systemic mycotoxicosis
- •Increased susceptibility to secondary infections
Who Is Most at Risk?
While mould can affect anyone, certain groups face significantly higher health risks from mould exposure.
Infants and young children
Developing lungs and immune systems are more vulnerable. Studies link early mould exposure to increased risk of developing asthma by age seven.
Elderly people
Weakened immune function and pre-existing respiratory conditions make older adults more susceptible to mould-related illness.
Asthma and allergy sufferers
Mould is a potent asthma trigger. The Australasian Society of Clinical Immunology and Allergy (ASCIA) identifies mould as a significant indoor allergen.
Pregnant women
Some studies suggest mycotoxin exposure during pregnancy may affect foetal development. Pregnant women should avoid mould exposure as a precaution.
Immunocompromised individuals
People undergoing chemotherapy, organ transplant recipients, and those with HIV/AIDS face serious risks from fungal infections caused by inhaling mould spores.
People with chronic lung disease
Conditions like COPD, cystic fibrosis, and bronchiectasis increase vulnerability to mould-related respiratory complications.
When to See a Doctor
You should see your GP if you experience:
- Persistent respiratory symptoms (cough, wheeze, shortness of breath) that worsen at home
- New or worsening asthma symptoms
- Unexplained skin rashes or chronic sinus infections
- Neurological symptoms such as persistent headaches, brain fog, or dizziness
- Symptoms that improve when you leave the property and return when you come back
Let your doctor know about potential mould exposure. They may refer you to an allergist or respiratory specialist for further assessment. Blood tests and skin prick tests can identify mould allergies.
When to Call a Professional vs. DIY
You Can Handle It Yourself If:
- ✓ The mould patch is smaller than 1 square metre
- ✓ It is on a non-porous surface (tiles, glass, sealed benchtop)
- ✓ No one in the household is in a high-risk group
- ✓ The cause is known and can be addressed (e.g., improve ventilation)
- ✓ You have no health symptoms
Call a Professional If:
- ✗ The mould covers more than 1 square metre
- ✗ It appears dark black or greenish-black (potential Stachybotrys)
- ✗ It has penetrated porous materials (plasterboard, carpet, timber)
- ✗ Anyone in the household is experiencing health symptoms
- ✗ There is a musty smell but no visible mould (hidden mould)
- ✗ Previous cleaning has not stopped regrowth
NSW Health Guidelines on Mould
NSW Health acknowledges that mould exposure can cause health problems and recommends the following:
- Fix water leaks and dampness issues promptly
- Ensure adequate ventilation in kitchens, bathrooms, and laundries
- Use exhaust fans when cooking, showering, and drying clothes
- Clean mould promptly when it appears
- Seek medical advice if mould-related health symptoms develop
For more information, refer to the NSW Health mould factsheet.
Frequently Asked Questions — Mould Health Risks
Can mould make you seriously ill?
Yes. While most people experience mild allergic symptoms, prolonged exposure to toxic mould species like Stachybotrys can cause serious respiratory illness, neurological symptoms, and immune suppression. Immunocompromised individuals face the greatest risk, including potentially life-threatening invasive fungal infections.
How quickly can mould affect your health?
Some people experience symptoms within hours of exposure, particularly those with mould allergies or asthma. For others, symptoms develop gradually over weeks or months of ongoing exposure. The speed of onset depends on the mould species, concentration of spores, and individual sensitivity.
Is the smell of mould dangerous?
The musty smell associated with mould is caused by microbial volatile organic compounds (MVOCs). While the odour itself is not directly toxic, it indicates active mould growth and the presence of airborne spores that can be inhaled. A persistent musty smell should be investigated even if visible mould is not apparent.
Can you live in a house with mould?
Living with mould is not recommended, especially for vulnerable groups. Even for healthy adults, ongoing exposure can lead to sensitisation and the development of new allergies. If mould cannot be removed immediately, ensure good ventilation, minimise time in affected rooms, and arrange professional remediation as soon as possible.
How do I know if mould is making me sick?
If your symptoms improve when you leave the building and worsen when you return, mould exposure may be the cause. Common signs include persistent respiratory symptoms, unexplained fatigue, headaches, and worsening allergies that do not respond to usual treatments. A GP can help assess whether mould exposure is contributing to your symptoms.
Does all mould produce mycotoxins?
No. Only certain mould species produce mycotoxins, and not all strains within those species produce them all the time. However, all mould produces allergens and irritants. You cannot determine whether mould is producing mycotoxins by sight alone — laboratory testing is required to identify species and toxin production.
What should I do if I find mould in my home?
For small patches (under 1 square metre) on non-porous surfaces, clean with a mould-specific product and improve ventilation. For larger areas, toxic species, or mould on porous materials, arrange a professional inspection and removal. Do not disturb large mould colonies without proper containment — this spreads spores throughout the property.
Are mould spores always present in the air?
Yes. Mould spores are naturally present in outdoor and indoor air. The concern arises when indoor spore concentrations become significantly elevated due to active mould growth inside the property. Professional air testing can determine whether indoor spore levels are abnormally high.
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