Mould Myths Explained: What Really Causes Mould in Homes (And What Actually Fixes It)
Mould Myths Explained: What Really Causes Mould in Homes (And What Actually Fixes It)
Mould is one of the most misunderstood problems in Australian homes. Many homeowners believe mould is caused by poor cleaning, old buildings, or “bad luck”, when in reality mould growth is almost always the result of excess moisture and poor ventilation.
These misconceptions lead to short-term fixes that don’t work, repeated mould outbreaks, and ongoing frustration. In this article, we break down the most common mould myths and explain what really causes mould — and how to stop it properly.
Myth 1: Mould Is Caused by Poor Cleaning
The truth:
Mould is not caused by dirt or lack of cleaning.
Mould spores exist naturally in outdoor and indoor air. They only become a problem when moisture levels remain high for extended periods. You can clean a surface perfectly and still have mould return if humidity and condensation are not controlled.
Bleach and mould sprays may remove visible mould temporarily, but they do not address the moisture that caused it. Without reducing humidity, mould will grow back.
Key takeaway:
Cleaning removes symptoms. Moisture control prevents mould.
Myth 2: Only Old or Poorly Built Homes Get Mould
The truth:
Modern homes are often more prone to mould than older ones.
New and renovated homes are built to be more airtight and energy efficient. While this improves heating and cooling performance, it also reduces natural air leakage that once allowed moisture to escape.
In airtight homes, moisture from everyday living becomes trapped unless deliberate ventilation is provided.
Common moisture sources include:
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Showers and baths
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Cooking
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Drying clothes indoors
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Breathing (people and pets)
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Damp subfloors
Without consistent ventilation, even a brand-new home can develop condensation and mould within months.
Key takeaway:
Mould is not an age problem — it’s a ventilation problem.
Myth 3: Opening Windows Is Enough to Prevent Mould
The truth:
Opening windows is unreliable and often ineffective.
Natural ventilation depends on:
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Weather conditions
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Wind direction
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Temperature differences
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Occupant behaviour
In winter — when mould and condensation are worst — windows are usually kept closed. Even when opened, windows do not guarantee moisture removal, especially overnight or during still weather.
Opening windows can also:
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Create cold draughts
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Increase heat loss
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Introduce pollen, dust, smoke, or outdoor pollution
Key takeaway:
Ventilation must be consistent and controlled — not weather-dependent.
Myth 4: Dehumidifiers Fix Mould Problems
The truth:
Dehumidifiers treat symptoms, not causes.
Dehumidifiers can temporarily reduce humidity, but:
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They only work while running
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Moisture returns once they’re turned off
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They don’t introduce fresh air
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They don’t remove CO₂ or pollutants
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They are often noisy and costly to run
Dehumidifiers are reactive devices. They do not stop moisture being generated, nor do they prevent condensation forming on cold surfaces throughout the home.
Key takeaway:
Dehumidifiers manage moisture after it builds up. Ventilation prevents it building up in the first place.
Myth 5: Mould Is Caused by Leaks Alone
The truth:
Leaks are only one of many moisture sources.
While plumbing leaks and water ingress can cause mould, many mould problems occur without any leaks at all. High indoor humidity from everyday living is enough to cause condensation on cold surfaces, leading to mould behind furniture, inside wardrobes, and on ceilings.
If mould appears seasonally — especially in winter — it is far more likely related to humidity and temperature differences than a hidden leak.
Key takeaway:
Not all mould is a leak issue. Most mould is a humidity issue.
Myth 6: Painting Over Mould Solves the Problem
The truth:
Painting over mould traps moisture and makes the problem worse.
Anti-mould paints may delay visible growth, but they do not remove moisture from the air or surfaces. In many cases, mould continues to grow behind the paint, eventually reappearing and causing further damage.
Painting should only occur after moisture levels are controlled and the affected area is properly dried.
Key takeaway:
Paint is cosmetic. Ventilation is preventative.
What Actually Causes Mould in Homes
Mould requires three things:
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Moisture
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Still air
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Time
When warm, moist air contacts cold surfaces and is not removed, condensation forms. If that moisture remains, mould will grow.
Common high-risk areas include:
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Bedrooms (overnight humidity)
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Bathrooms
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Laundries
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South-facing rooms
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Behind furniture
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Wardrobes
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Poorly ventilated subfloors
The Real Solution: Proper Ventilation
The most reliable way to prevent mould is to control moisture at the whole-home level.
Effective ventilation:
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Removes moisture continuously
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Prevents condensation forming
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Reduces indoor humidity
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Improves air movement
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Maintains healthier indoor air quality
Depending on the home, this may include:
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Whole-home ventilation systems
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Balanced ventilation with HRV or ERV
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Subfloor ventilation to reduce rising moisture
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Properly designed bathroom and kitchen extraction
Ventilation works with the way air behaves, rather than trying to fight moisture after damage has already occurred.
Final Takeaway: Stop Treating Mould — Start Preventing It
Mould is not caused by poor cleaning, bad habits, or old buildings. It is caused by uncontrolled moisture in poorly ventilated homes.
If mould keeps returning, the problem is not the mould itself — it’s the environment that allows it to grow.
By addressing ventilation and moisture control properly, mould stops being a recurring issue and becomes something you don’t have to think about at all.