A persistent musty smell means there is damp and, very likely, mould growing somewhere in the building, often where you can’t see it. Whether that smell has anything to do with headaches or tiredness is a medical question for your GP: Australian health guidance links mould mainly to respiratory and allergy symptoms, and the evidence for other effects is described as inconclusive. What you can do in parallel is find and fix the source, because that is the step every health authority recommends.
What health authorities actually say
NSW Health’s mould factsheet lists the common health effects of mould as a runny or blocked nose, irritation of the eyes and skin, and sometimes wheezing, with asthma attacks possible in people with asthma. It also says most people will not experience any health problems from contact with mould. People with asthma, allergies or other breathing conditions may be more sensitive.
The Western Australian Department of Health’s 2024 review, Indoor Mould: Health Risk Assessment and Management, finds that indoor mould exposure is associated with respiratory effects, but that evidence for other health impacts, including non-respiratory effects, is currently insufficient or inconclusive.
So headaches and fatigue are not on the official symptom lists, and they have many possible causes. That does not mean your symptoms aren’t real; it means the right person to work out why you feel unwell is your GP. Tell them about the smell, how long it has been there, and whether you feel better when you are away from home. Fixing the building is worth doing regardless, because damp and mould are worth removing for everyone.
Why mould smells musty
The smell comes from gases called microbial volatile organic compounds, released as mould grows and breaks down material. Strength of smell doesn’t track the size of the problem: a small colony in a sealed wall cavity can smell stronger than a larger patch in a well-aired room, because the gas concentrates before it escapes.
Where the smell usually starts
| Where it is strongest | Likely source | First check |
|---|---|---|
| Ground-floor rooms, especially in the morning | Damp subfloor | Torch through a subfloor vent or hatch for white or dark growth on bearers and joists |
| When the air conditioning starts | Mould in the unit or ducts | Filter and drip tray; see black mould in air conditioners |
| Ceiling area, after rain | Roof leak wetting insulation | Roof space, if safe to access, for wet batts and staining |
| One room, worse after rain | Water entering a wall | Outside face of that wall: flashing, weep holes, cracked render, gutters |
| Next to a bathroom or laundry | Leaking shower or failed waterproofing | Swollen skirtings, loose tiles, staining on the other side of the wall |
| Whole house, worst in winter | Condensation mould on cold walls | Behind wardrobes and beds on external walls |
| One patch of carpet | Old water damage under the floor covering | Lift a corner if a leak or flood once reached that spot |
The musty smell in house guide goes through these sources in more detail.
A simple way to narrow it down
- Keep a short log for a few days. Note morning versus evening, which rooms, and whether it changes after rain or when heating or cooling runs.
- Check the easy places. Under sinks, bathroom and laundry cabinets, behind furniture on outside walls, and the air conditioner filter.
- Look underneath and above if you safely can. The subfloor through a vent or hatch, and the roof space from the manhole. Don’t crawl into either if you are unsure about access, footing or wiring.
- Check the outside after rain. Overflowing gutters, blocked subfloor vents, garden beds banked against walls, and downpipes discharging next to the house.
Older timber-floored houses across the northern suburbs often have subfloors with too little cross-ventilation; the subfloor ventilation guide explains how to assess that.
When to get an inspection
Book a mould inspection and moisture investigation when:
- You can smell mould but can’t find growth after a reasonable search
- The smell persists despite airing and cleaning
- You’ve found a likely source but don’t know how far it goes
- Your GP has asked about the home environment
- You are buying, selling or renting and need documentation
An inspector uses moisture meters to measure damp in building materials and thermal imaging to show hidden wet areas, then sets out the cause and a scope of works in a written report. Where the source turns out to be under the floor or in the ceiling, that is the job of subfloor and roof void mould remediation.
Air fresheners only mask the smell. A HEPA air purifier can reduce airborne particles in one room, but it doesn’t remove the growth producing them.
Next step
Describe the smell, where it is strongest and your suburb on the contact form. The enquiry is passed to an independent local professional who can say whether an inspection or a direct remediation quote is the right starting point. For symptoms, see your GP.
Frequently asked questions
Can mould cause headaches and fatigue?
NSW Health lists mould’s common effects as nose, eye and skin irritation and sometimes wheezing, and the WA Department of Health describes evidence for non-respiratory effects as inconclusive. Headaches and tiredness have many causes, so see your GP and mention the musty smell.
Is a musty smell without visible mould a problem?
Usually it means damp and mould are present somewhere you haven’t looked, such as a wall cavity, under flooring, or in the subfloor or roof space. It is worth finding and fixing.
Can mould inside walls make the whole house smell?
Yes. The gases travel through gaps around pipes, cables, plasterboard joints and floor vents, so a smell in several rooms often points to one hidden source rather than several patches.
Can my air conditioner spread a mould smell?
Yes. Mould on the coil or in the drip tray is blown into the room when the unit runs. If the smell starts when the system starts, check the unit first.
Will an air purifier get rid of a musty smell?
Only partly. A unit with an activated carbon stage can reduce the odour and a HEPA filter captures airborne spores, but neither removes the growth, so the smell returns until the source is fixed.