Perth’s grass pollen season starts in September and runs through to December. If you get hay fever, sneezing fits, or itchy eyes every spring, you’ve probably blamed the pollen outside. But there’s a good chance your air conditioner is playing a role too — and not in the way you’d think.
Your aircon doesn’t cause allergies. But a system that’s carrying dust, mould, or old pollen from last season can make symptoms noticeably worse the moment you turn it on. Here’s how it happens, and what to check before spring arrives.
How Your Air Conditioner Can Make Allergies Worse
Air conditioners don’t manufacture allergens — but they do something arguably worse: they recirculate them, continuously, through every room the system serves.
Here’s the mechanism. Your system pulls air in through the return air intake, passes it across the filter and coil, and pushes it back out through the vents. If that filter is dirty, or if dust, mould, or pollen has settled inside the ductwork or on the coil itself, the system isn’t cleaning the air — it’s actively distributing whatever’s built up inside it.
Dust mites and dust mite allergens accumulate in ductwork and on filters over time, particularly in ducted systems that haven’t been serviced recently.
Mould spores are a genuine risk inside air conditioning systems — the evaporator coil is a cold, damp surface, which is exactly the environment mould needs to establish. Once mould is present on the coil or inside the ducting, every cycle of the system sends spores into the air you breathe.
Old pollen from previous seasons can sit inside ductwork and filters for months. If your system wasn’t cleaned before or after last spring, that pollen doesn’t just disappear — it’s still in there, waiting for the system to run again.
Pet dander, tracked-in dust, and general household particulates all follow the same path — pulled into the return air, and pushed back out through every vent in the home.
1. A Dirty Filter Is the First Thing to Check
This is the simplest and most common contributor. A clogged filter does two things badly: it lets fine particles bypass it and circulate through the home, and it restricts airflow, forcing the system to work harder.
Standard filters catch larger particles like dust and pet hair reasonably well, but a filter that’s overdue for cleaning or replacement loses even that basic effectiveness. For households with allergy sufferers, a higher-rated filter — designed to capture finer particles including pollen — makes a measurable difference, provided it’s changed on schedule.
💡Pro Tip
Check your filter now, before pollen season starts. If it’s visibly grey, clogged, or hasn’t been checked in the last few months, clean or replace it before spring — not after symptoms have already started.
2. Mould on the Evaporator Coil Is a Common Hidden Cause
This is the one most Perth homeowners don’t think to check. The evaporator coil — inside the indoor unit — is cold and damp by design. That’s exactly the environment mould needs to grow.
If your system produces a musty smell when it first starts, especially after a period of not being used, mould on the coil or inside the unit housing is a likely cause. That musty smell isn’t just unpleasant — it’s a sign that mould spores are being released into the airflow every time the system runs.
Perth’s coastal humidity and the transition from Perth’s damp winter into warmer spring conditions creates favourable conditions for this kind of growth, particularly in systems that haven’t had a professional clean recently.
3. Ductwork Can Hold onto Last Season’s Pollen
If your ducted system wasn’t cleaned before or after last spring’s pollen season, there’s a real chance some of that pollen is still sitting in the ductwork. Pollen grains are small and light — exactly the kind of particulate that settles in duct runs and accumulates over time.
When the system starts running more in spring — as households switch from heating to cooling, or just run the system more with warmer days — any pollen residue in the ducts gets stirred up and redistributed through the home.
This is particularly relevant if:
- The system hasn’t been cleaned in more than 2–3 years
- You noticed worse allergy symptoms at home last spring specifically
- Vent grilles show visible dust buildup
- No one recalls the last time the ducts were professionally cleaned
4. Closed Windows Trap Indoor Allergens — But Only If the System Is Clean
There’s a common piece of advice for allergy sufferers during pollen season: keep windows closed and run the air conditioner instead of letting outdoor air in. This is genuinely good advice — but only if the system itself isn’t the problem.
A clean, well-maintained air conditioner running with windows closed is one of the most effective ways to reduce pollen exposure indoors during Perth’s spring. A dirty system doing the same thing just swaps outdoor allergens for indoor ones.
This is the key distinction: the goal isn’t to avoid using your aircon during pollen season — it’s to make sure it’s clean before you rely on it more heavily.
Signs Your Aircon Is Contributing to Allergy Symptoms
- Symptoms are worse at home than elsewhere: If sneezing, itchy eyes, or a stuffy nose consistently ease up when you’re out of the house, indoor air quality is worth investigating.
- Symptoms start or worsen shortly after the system turns on: This is one of the clearest indicators — if allergy symptoms flare up specifically when the aircon starts running, particularly at the beginning of a cooling season, the system itself is a likely contributor.
- A musty smell from the vents: This usually points to mould inside the unit or ductwork — a direct allergen source.
- Visible dust around vent grilles: A grey or brown ring around a vent is a sign the system is distributing accumulated material into the room.
- It’s been more than 2 years since the last professional clean: Time alone is a reasonable predictor — the longer since a full clean, the more has likely accumulated.
What to Do Before Spring Hits Perth
Perth’s grass pollen season typically begins in September and builds through November. The best time to address a system that might be contributing to allergies is before that season starts — not once symptoms are already flaring.
▪️ Check and clean or replace filters now: This is the simplest step and makes an immediate difference.
▪️ Book a professional duct and system clean if it’s overdue: If your ducted system hasn’t been cleaned in 2–3 years, or you’re not sure when it was last done, get it assessed before spring.
→ Read more: How Often Should You Clean Your Air Ducts? A Perth Homeowner’s Guide
▪️ Have the indoor unit checked for mould if there’s a musty smell: A professional clean and sanitise removes mould from the coil and housing rather than just masking the smell.
▪️ Consider whether duct cleaning is actually warranted for your situation: Not every home needs it every year — but allergy sufferers heading into pollen season are one of the clearest cases where it makes a real difference.
→ Read more: Is Air Duct Cleaning Worth It? The Honest Answer for Perth Homes
Quick Reference — Allergy Season Aircon Checklist
| Check | Why it matters |
|---|---|
| Filter condition | Dirty filter = more particles circulating, harder-working system |
| Musty smell on startup | Likely mould on coil or in ductwork |
| Time since last duct clean | 2+ years means likely accumulation of dust, pollen, dander |
| Symptoms worse at home | Direct indicator of indoor air quality issue |
| Vent grille dust rings | Visible sign of system distributing debris |
| Windows closed but symptoms persist | System itself may be the source |
The Bottom Line
Your air conditioner isn’t the cause of your allergies — but a dirty one can absolutely make them worse. A clean filter, a mould-free coil, and ducts that aren’t holding onto last season’s pollen make the difference between an aircon that helps you get through spring and one that’s working against you. Checking these now, before pollen counts rise, is the simplest way to head into Perth’s spring with one less allergy trigger in the house.
At Air Cool Care, we clean and service air conditioning systems and ductwork across Perth — from Joondalup and Wanneroo in the north to Cockburn, Rockingham, and Armadale in the south. If allergy season has been rough in your home before, getting the system checked now — before pollen levels rise — is the best time to act.
Related Reading
- How Often Should You Clean Your Air Ducts? A Perth Homeowner’s Guide
- Is Air Duct Cleaning Worth It? The Honest Answer for Perth Homes
- 10 Common Causes of Poor Indoor Air Quality
- How to Fix Black Mould in Air Vents
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