Mould in the Home: Causes, Health Risks, Types, Cleaning and Prevention
The Complete Guide to Safe, Professional Mould Removal
Mould is one of those problems that sneaks up quietly and then refuses to leave. First it is a faint musty smell. Then a few dark dots above the shower. Next thing you know, whole walls are spotted, the air feels heavy, and someone in the house cannot stop coughing.
Mould is not just ugly. It damages buildings. It degrades air quality. And in the wrong conditions, it can absolutely impact health.
If you want a straight-shooting, science-backed, real-world guide to mould causes, mould health risks, types of mould, safe mould cleaning, professional mould removal and mould prevention, you are in the right place.
This guide is written for homeowners, renters, property managers and anyone searching for professional mould cleaning services in Australia.
What Causes Mould in Homes and Buildings?
Mould is a fungus. The spores are already everywhere in the air. They only turn into a visible infestation when three factors line up: moisture, food and time.
Take moisture away and mould cannot grow. It is that simple.
The most common causes of indoor mould are leaking roofs, gutters and plumbing, poor bathroom ventilation, steamy showers with no exhaust fan, high indoor humidity, condensation on cold windows and walls, flooding or overflow events that were not dried properly, blocked subfloor ventilation, and air conditioning systems with dirty coils or drain lines.
Once moisture sits on plasterboard, timber, carpet underlay or insulation for 24 to 48 hours, mould can establish itself. After that, wiping the surface does not solve the root problem. You must remove moisture or mould always comes back.
Why Mould Is Bad for Your Home
Mould does not just stain surfaces. It feeds on building materials.
Over time, it can weaken plasterboard, rot timber framing, destroy carpet backing and underlay, permanently stain walls and ceilings, and damage insulation and reduce its effectiveness.
Long-term mould issues often turn into expensive rectification jobs, not just cosmetic clean-ups. This is why early intervention always saves money.
Why Mould Is Bad for Your Health
This is where mould stops being a cleaning issue and becomes a medical one.
Mould releases spores, fragments, gases and sometimes mycotoxins. These become airborne and are inhaled into the sinuses and lungs.
Common symptoms of mould exposure include sneezing, coughing, throat irritation, runny or blocked nose, eye irritation and redness, skin rashes, fatigue and headaches, brain fog and poor concentration, and asthma flare-ups and wheezing.
People at higher risk include children and infants, elderly people, anyone with asthma or allergies, and anyone undergoing chemo or immune suppression.
Some moulds can produce mycotoxins. Under prolonged exposure, these have been linked in research to neurological symptoms, inflammation and, in extreme cases, lung injury. You cannot identify toxic mould with your eyes. All visible mould should be treated seriously.
The Most Common Types of Indoor Mould
You will not normally know the exact species without laboratory testing, but these are the most common mould groups found in Australian homes.
Cladosporium
Dark green, brown or black. Velvety texture. Common on window sills, painted timber and fabrics. A major allergy trigger but usually not highly toxic.
Penicillium
Blue-green or dusty green. Loves carpets, wallpaper, mattresses and water-damaged furnishings. Can trigger asthma and allergies. Some strains produce mycotoxins.
Aspergillus
Often grey, yellow-green or powdery. Found in dust, air conditioning systems and wall cavities. Can cause serious respiratory infections in vulnerable people.
Stachybotrys (‘Black Mould’)
Thick, dark green to black, slimy when wet, strong musty smell. Grows on soaked plasterboard, ceiling tiles and timber. Known for potential mycotoxin production. Indicates a long-term moisture problem.
It’s important to remember that black mould is not the only dangerous mould. All indoor mould is unhealthy and must be removed safely.
How Mould Enters the Body and Makes You Sick
The main exposure pathway is breathing contaminated air. Spores and mould fragments enter the sinuses, airways and lungs. From there, they trigger inflammatory immune reactions, allergic responses and asthmatic airway constriction.
In rare cases and high exposure environments, mould-related particles may also impact neurological function, contributing to cognitive symptoms.
Skin contact can cause irritation and rashes. Eye exposure causes burning and redness. Ingestion is rare indoors but can occur through surface contamination.
PPE for Safe Mould Cleaning and Removal
Anyone doing mould cleaning should wear a P2 or N95 respiratory mask, sealed safety goggles, nitrile or rubber gloves, long sleeves and long pants, disposable coveralls for large jobs, and closed shoes or rubber boots.
Never clean mould with bare hands, no mask, open cuts on skin, or clothing you intend to keep clean.
How to Clean Mould Safely and Properly
There is no shortcut. Proper mould removal is a process.
Step 1 - Fix the Moisture
No leak fixed means mould returns.
Step 2 - Decide What Can Be Saved
Hard surfaces can be cleaned. Soft materials like soaked plasterboard, ceiling tiles, underlay and insulation usually must be removed and replaced.
Step 3 - Use the Right Cleaning Agents
Effective household cleaners include white vinegar used undiluted, 3% hydrogen peroxide, and detergent with warm water for light surface mould.
A professional-grade option is Concrobium Mold Control, a non-bleach spray that kills mould and leaves a protective barrier.
Bleach can remove stains on tiles and hard surfaces but is not recommended for porous materials and carries chemical risks.
Step 4 - Cleaning Technique
Lightly mist mould before disturbing it. Wipe growth away with disposable cloths. Apply cleaner and allow contact time. Scrub. Rinse if required. Dry thoroughly with airflow.
Any job larger than roughly one square metre, or with confirmed black mould inside walls or ceilings, often requires removal and replacement of affected wall linings or ceiling panels, not just surface cleaning.
Step 5 - Monitoring
Once cleaning is completed, the environment should be monitored closely. Persistent musty smells, visible regrowth, or water staining are early warning signs that mould may still be active behind surfaces.
Occupant health is another key indicator. Ongoing coughing, sinus irritation, fatigue, headaches or cognitive symptoms such as brain fog after cleaning can suggest continued exposure and should trigger further investigation.
Mould commonly takes hold inside wall cavities, ceiling voids, wet insulation and under carpets where moisture becomes trapped. In these cases, building repairs are usually required, including replacement of affected wall panels, insulation and floor coverings to fully resolve the contamination.
How to Prevent Mould from Coming Back
This is where 90% of long-term success lives.
Keep indoor humidity between 30 and 50 percent. Use exhaust fans in bathrooms and kitchens. Run dehumidifiers in damp spaces. Fix leaks immediately. Dry wet areas within 24 hours. Use mould-resistant paint and sealants. Maintain gutters and exterior drainage. Avoid carpet in bathrooms and basements.
Mould prevention is environmental control, not chemical warfare.
Outdoor Mould vs Indoor Mould
Outdoor mould is normal and unavoidable. It lives in mulch, gardens, soil and air. Problems occur when moisture lets that outdoor mould colonise indoor building materials.
Good drainage, sealing, ventilation and humidity control stop that crossover.
Final Word: Why Professional Mould Cleaning Matters
This is the honest truth most websites won’t tell you.
Mould removal is not just spray and wipe. It is moisture control, safe removal, contamination management and prevention strategy.
Do it poorly and mould returns. Do it unsafely and health suffers. Do it professionally and the problem actually ends.
If you are dealing with repeating bathroom mould, musty air smells, ceiling or wall black mould, rental property mould disputes, or post-flood mould, it is time to treat it properly.
This is where professional cleaning services like Leronay step in. Not just to remove the visible mould, but to stop the cycle permanently.