Your aircon could be circulating thousands of mould spores every time it runs.
Most people only notice mould when they spot it on a wall or ceiling. But aircon mould spores are invisible, and your air conditioning system is one of the most overlooked sources of spore spread in Australian homes.
Below, we cover the visual, smell, and health warning signs that your aircon has a mould problem, where mould hides inside the unit, and why wiping it down won’t fix it.
If you notice signs of mould exposure from your air conditioning system, book a free mould inspection with Mould and Hygiene Solutions. We service Newcastle, the Central Coast, Lake Macquarie, Hunter Valley and Port Stephens.
What aircon mould spores actually are
Mould spores are microscopic reproductive cells released by mould colonies. When mould grows inside your air conditioning system, the fan pushes those spores out through the vents and into every room the system reaches.
A single colony can release millions of spores per day. At 1 to 30 microns, they’re far too small for your aircon’s standard filter to catch.
The species most commonly found inside Australian air conditioners are Aspergillus, Cladosporium, and Penicillium. They produce different sized spores and carry different health risks, but all of them love the dark, damp conditions inside an aircon unit.
So even when the unit looks clean from the outside, the air passing through it can carry a concentrated load of spores straight into your living space. In humid areas like Newcastle and the Central Coast, this problem builds fast.
- Spores are 1-30 microns, invisible to the naked eye
- Standard aircon filters don’t catch most mould spores
- A single colony can release millions of spores daily
- Spores land on surfaces throughout the home and start new colonies
- Condensation inside the unit provides constant moisture for growth
Wiping down visible mould inside the unit only deals with what you can see. Spores embedded in the evaporator coil, drain pan, and ductwork lining stay put and keep circulating. Knowing what actually kills mould spores matters more than knowing how to clean surfaces.
Warning signs your aircon is spreading mould spores
Mould inside an air conditioning system rarely shows up as a visible patch on the wall. Instead, it announces itself through subtler signs that most homeowners write off as normal wear or seasonal allergies.
Catching these early makes a real difference. By the time you can actually see mould on a vent grille, the colony inside the unit is already well established and pumping out spores.
- Musty or damp smell when the aircon runs – the most reliable early indicator, caused by volatile organic compounds released by active mould
- Black or dark spots around air vents – mould colonies forming where moist air exits the system
- Visible mould on filters or inside the unit – fuzzy grey, black, or green patches on any internal surface
- Increased allergy symptoms indoors – sneezing, itchy eyes, runny nose, or throat irritation that improves when you leave the house
- Respiratory flare-ups in family members – coughing, wheezing, or chest tightness, particularly in children or anyone with asthma
- Condensation or water stains around the unit – a sign the drain line may be blocked or the unit isn’t dehumidifying properly
- A film or residue on surfaces near vents – fine particulate matter settling on furniture below air outlets
If you notice two or more of these signs, the mould has likely been growing for weeks. A professional mould test can confirm spore levels in your air.
Spraying the vent or filter with a retail mould cleaner only touches the visible growth. The colony inside the coil and drain pan keeps producing spores regardless.
Health symptoms linked to aircon mould spores
Breathing in mould spores from your aircon can cause anything from mild irritation to serious respiratory problems. How bad it gets depends on your exposure level, how long the mould has been there, and your own sensitivity.
People with asthma, allergies, or weakened immune systems cop it worst, but prolonged exposure affects healthy adults too. NSW Health notes that inhaling mould spores can trigger asthma attacks and cause nasal congestion, eye irritation, and skin reactions. The Better Health Channel adds that people with chronic lung conditions face a higher risk of mould-related infections.
| Symptom | Short-term exposure | Prolonged exposure |
|---|---|---|
| Nasal congestion | Occasional stuffiness | Chronic blocked nose |
| Coughing | Dry cough when aircon runs | Persistent cough, day and night |
| Eye irritation | Occasional itchiness | Red, watery eyes daily |
| Throat irritation | Scratchy throat | Chronic sore throat |
| Skin reactions | Mild or none | Rashes or dermatitis |
| Fatigue | Mild tiredness | Constant fatigue, brain fog |
| Headaches | Occasional | Frequent and unexplained |
The giveaway is that symptoms appear or get worse when the aircon is running and ease off when you step outside or go to a different building. Plenty of homeowners across Newcastle and the Hunter Valley spend months popping antihistamines when the real culprit is mould growing inside their air conditioner.
No amount of filter cleaning or vent wiping will fix these symptoms while the colony inside the unit stays active.
Where mould hides inside your air conditioner
Mould doesn’t grow on the parts of your aircon you can easily see or reach. It sets up in the dark, damp spots inside the unit where condensation gives it a constant water source.
That’s why wiping the filter or spraying the vent grille with bleach never solves the problem. The mould you can get to is just the outermost edge of a colony that extends deep into components you’d need to partially disassemble to reach.
- Evaporator coil – the metal fins collect condensation constantly, keeping the surface permanently damp
- Drain pan and drain line – standing water from condensation makes this a prime breeding ground
- Blower fan and housing – mould attaches to fan blades and gets flung directly into the airflow
- Ductwork lining – insulation inside ducts absorbs moisture, and mould grows within the material itself
- Behind the filter – the gap between the filter slot and evaporator coil is a dead zone most people never check
None of these spots are accessible with a cloth and a spray bottle. Retail mould products can’t reach evaporator coil fins or penetrate ductwork lining where the mould’s root structure has embedded itself.
How mould grows differently in split systems and ducted units
Split systems and ducted air conditioners both grow mould, but the contamination patterns are different. What you need to check depends on which system your home has.
In a wall-mounted split system, mould concentrates in the indoor head unit. The blower wheel, evaporator coil, and drain tray all sit behind the front panel, and they accumulate mould when condensation lingers after the cooling cycle ends. You might notice water dripping from the unit, or a musty smell within seconds of switching it on.
Ducted systems spread the problem much further. The fan coil unit sits in the roof space or under the floor, connected to every room through insulated ductwork.
Once mould takes hold at the source unit, spores travel through the entire duct network and come out at every vent in the house. The insulation lining inside the ducts can harbour mould for months with no visible sign at the vent grilles.
| Factor | Split system | Ducted system |
|---|---|---|
| Mould location | Indoor head unit (blower, coil, tray) | Fan coil unit + full duct network |
| Spread pattern | One room or zone | Every room connected to the system |
| Visibility | Sometimes visible behind front panel | Hidden in ceiling or floor cavity |
| DIY access | Limited (filter and front panel only) | Almost none without professional tools |
| Treatment scope | Single unit | Source unit plus all ductwork |
For either system, running the aircon on fan-only mode for 15 to 20 minutes after cooling helps dry out internal surfaces and slow mould growth. But once a colony has taken hold, drying alone won’t get rid of it.
Why DIY aircon mould cleaning doesn’t work
Homeowners across the Central Coast and Lake Macquarie regularly try to handle aircon mould themselves before calling anyone. It seems straightforward: buy a mould spray, open the unit, clean what you can see, swap the filter.
The problem is that this only treats the surface while leaving the root structure intact. Mould roots (hyphae) penetrate into the substrate material, whether that’s coil fins, the drain pan, or ductwork lining.
You’ll remove the visible growth, but regrowth from the embedded roots typically shows up again within two to six weeks.
Common DIY methods and why they fail
- Bleach spray on vents – kills surface mould on contact but has zero effect on mould inside the coil or drain pan
- Filter replacement – cleaning or replacing your aircon filter removes trapped spores but does nothing about the colony producing them
- Vinegar or tea tree oil – natural antimicrobials that can’t penetrate metal coil fins or ductwork insulation
- Retail mould killer sprays – designed for bathroom tiles and grout, not HVAC components
- Wiping the fan blades – removes visible mould from one component while ignoring the rest
Disturbing mould without proper containment can make things worse. Scrubbing or spraying releases a burst of spores into the air, potentially spreading contamination to other rooms. Professional mould remediation uses containment barriers to prevent cross-contamination.
The thing DIY mould removal misses entirely is why the mould is growing. Your aircon grows mould because of excess condensation, poor drainage, or humidity imbalance. Until you fix that underlying cause, any cleaning is temporary.
How to reduce mould growth in your aircon
Prevention won’t replace professional treatment when mould is already there. But these steps slow regrowth after treatment and reduce the chance of a new colony forming.
- Run fan mode after cooling – leave the fan running for 15 to 20 minutes after the cooling cycle ends. This dries out the evaporator coil and drain pan, removing the moisture mould needs.
- Keep indoor humidity below 60% – a hygrometer costs under $20 and tells you exactly where you stand. If your home regularly sits above 60%, a dehumidifier helps. The humidity level that actually prevents mould is lower than most people think.
- Improve ventilation – bathrooms, laundries, and kitchens push moisture into the air that your aircon then circulates. Exhaust fans and open windows during cooking or showering make a real difference. Good ventilation does more to prevent mould than any amount of surface cleaning.
- Get annual professional servicing – a yearly inspection catches mould before it grows into a colony large enough to affect air quality.
- Don’t block return air grilles – restricted airflow forces the system to work harder and increases condensation on the evaporator coil.
These habits extend the life of a professional treatment, but they can’t replace one. Once mould has embedded into the coil or ductwork, no amount of fan time or humidity control will remove it.
How professional aircon mould treatment works
Professional mould treatment for air conditioning systems goes well beyond surface cleaning. Mould and Hygiene Solutions uses an Australian-made, non-hazardous, non-corrosive and environmentally friendly antimicrobial solution that penetrates into the substrate where mould roots are embedded.
That’s the difference between wiping off what you can see and actually eliminating the mould colony, including the microscopic root network that surface methods can’t reach. The treatment comes with an unconditional 12-month mould-free guarantee.
- Full inspection of the air conditioning system, including evaporator coil, drain pan, blower fan, and accessible ductwork
- Air quality testing to measure spore levels before treatment
- Containment setup to prevent spore release during treatment
- Application of antimicrobial solution to all affected components, penetrating coil fins and substrate material
- Drainage system check to eliminate the moisture source
- Post-treatment air quality test to confirm spore reduction
- Written 12-month guarantee against mould regrowth
The antimicrobial solution keeps working after application, creating a protective barrier that prevents recolonisation. Bleach, by comparison, evaporates within minutes and leaves the surface completely unprotected.
When to book an aircon mould inspection
Don’t wait until you can see mould growing out of your vents. If your aircon produces a musty smell, if allergy symptoms spike when the system runs, or if anyone in the household has unexplained respiratory issues, get the system inspected before things get worse.
- Your aircon smells musty or damp when it starts up
- Allergy or respiratory symptoms worsen indoors
- You can see black spots on vents, filters, or inside the unit
- The system hasn’t been professionally serviced in over 12 months
- Your home is in a high-humidity area like Newcastle, the Central Coast, or Lake Macquarie
- Previous DIY cleaning hasn’t stopped the smell or symptoms from coming back
Mould and Hygiene Solutions offers free inspections across Newcastle, the Central Coast, Lake Macquarie, Hunter Valley and Port Stephens, no obligation. If mould is found, the treatment uses the same antimicrobial solution and comes with the 12-month guarantee.
Every week you wait is another week of spores circulating through your home. The mould removal process is faster and less disruptive than you’d think.
Frequently asked questions about aircon mould spores
Does air conditioning kill mould spores?
No. Air conditioning cools and dehumidifies air, but it doesn’t kill mould spores. The cooling process actually creates condensation inside the unit, which gives mould the moisture it needs to grow.
Running your aircon can reduce humidity in the room, but if the unit itself is contaminated, it’s actively distributing spores while it runs.
Is aircon mould harmful to your health?
Yes. Breathing in mould spores can trigger asthma attacks, allergic reactions, sinus congestion, and chronic coughing. People with respiratory conditions, compromised immune systems, or young children are most at risk.
The longer the exposure, the worse it gets, which is why an aircon running for hours each day is such an effective delivery system for spores.
How long do mould spores stay in the air after cleaning?
Disturbed mould spores can stay airborne for several hours in a still room. With air circulation from a fan or aircon, they spread further but also settle faster on surfaces. Professional treatment uses containment barriers during cleaning specifically to stop spores dispersing through the rest of the house.
Can I still use my aircon if it has mould?
You can, but every time you turn it on, you’re pushing mould spores into your living space. If anyone in the household has asthma or allergies, it’s worth switching to fans or opening windows at night until the system has been professionally treated.
How often should I have my aircon cleaned to prevent mould?
Once a year at minimum. Homes in high humidity areas like the Hunter Valley and Central Coast, or households that run the aircon daily during summer, benefit from servicing every six months. That way you catch early mould growth before it becomes a colony large enough to affect air quality.
Can I clean mould from my aircon myself?
You can clean the filter and wipe the front panel, but that’s about as far as most homeowners can safely go. The evaporator coil, blower wheel, drain pan, and ductwork all need professional tools and training to access. Scrubbing visible mould without containment can release a burst of spores and spread contamination to other rooms.
Why does my aircon smell musty even after cleaning?
Because the mould you cleaned was only the visible outer edge of the colony. The root structure (hyphae) embeds into the coil fins, drain pan, and duct lining where a cloth or spray can’t reach. The musty smell comes from volatile organic compounds the active colony releases, and it won’t go away until the entire colony is eliminated with an antimicrobial treatment.
How does mould form in a split system air conditioner?
During cooling, the evaporator coil drops below the dew point of the surrounding air, so moisture condenses on the coil and drips into the drain pan. If the drain line is slow, partially blocked, or the unit stays damp after the cooling cycle ends, mould colonises these wet surfaces within days. Dust and skin cells trapped in the filter give the colony extra food to feed on.
What is the difference between mould and mildew in an aircon?
Mildew is a surface fungus that sits on top of materials and wipes off easily. Mould penetrates into the substrate and sends root structures (hyphae) deep into porous surfaces.
What grows inside aircon units is almost always mould, not mildew, because the damp conditions inside coils and drain pans support the deeper-rooting organism. Knowing the differences between mildew and mould helps you work out which problem you’re dealing with.
Stop breathing in what your aircon is blowing out
Your air conditioner should cool your home, not fill it with mould spores. If you’ve noticed a musty smell, unexplained allergy symptoms, or dark spots around your vents, mould inside your air conditioner is the most likely cause.
DIY cleaning can’t reach the root structure embedded inside evaporator coils, drain pans, and ductwork. Professional treatment with a proven antimicrobial solution is the only way to eliminate the problem and stop it coming back.
If you’re in Newcastle, the Central Coast, Lake Macquarie, Hunter Valley or Port Stephens, book a free inspection with Mould and Hygiene Solutions today. We’ll check your system, find the source, and give you a straight answer on what needs to happen.
