Why Your Home Smells Musty and What to Do About It

A musty smell in the home is one of those things that you can stop noticing because you live with it every day — until a visitor walks in and it becomes suddenly obvious. Or you've come back after a holiday and it hits you as soon as you open the door.

The instinct is to light a candle, buy a plug-in freshener, or spray something around. But a musty smell is almost never just a smell — it's a symptom. Something is producing it, and until you find and fix the source, no amount of fragrance will solve the problem. It will just make your home smell like musty lavender instead of just musty.

This guide walks through the most common causes of musty smells in Adelaide homes, how to identify which one you're dealing with, and what to actually do about it.

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What Causes the Musty Smell?

The musty smell has a specific chemistry. It's produced primarily by microbial volatile organic compounds (MVOCs) — gases released by mould and mildew as they grow and digest organic material. Different mould species produce different MVOCs, which is why musty smells vary slightly — some earthy, some damp, some more pungent.

The bottom line: a musty smell means there is mould or mildew somewhere. It might be visible. More often, it's not.

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The Most Common Sources in Adelaide Homes

1. Mould Behind or Under Surfaces

This is the most serious and most common source of persistent musty smell. Mould growing behind walls (from plumbing leaks, condensation or water ingress), under flooring (from subfloor moisture), or inside ceiling cavities (from roof leaks) produces strong musty odour without any visible mould in the living spaces.

Signs:

• Musty smell that doesn't improve with ventilation
• Smell concentrated in a specific area of the home
• History of any water leak, roof issue or plumbing problem
• Peeling paint or wallpaper (sign of moisture behind the wall)
• Discolouration on walls or ceiling
• Unexplained respiratory symptoms that improve when you leave the home

What to do: This is not a cleaning problem — it's a building problem. You need to find and fix the moisture source (leak, condensation, rising damp) and then remediate the mould properly. Surface cleaning will not fix mould inside walls. If you suspect this is the source, engage a building inspector or mould assessor.

2. Front-Load Washing Machine Seal

The single most common cause of musty smell in modern homes that people don't immediately identify. The rubber door seal on front-loader washing machines stays damp between cycles and develops significant mould growth — often black or grey — in its folds and crevices.

Signs:

• Musty smell strongest in the laundry or adjacent rooms
• Washing comes out with a musty smell even after being freshly washed
• Visible grey or black mould in the folds of the door seal
• Smell that gets stronger after a wash cycle

What to do: Clean the door seal thoroughly with an old toothbrush and diluted bleach solution (1 part bleach to 10 parts water). Get into every fold. Run a hot empty cycle with a washing machine cleaner. Going forward: wipe the seal dry after every wash, leave the door open between cycles to allow drying, and clean the seal monthly.

3. Carpet

Old carpet — particularly carpet that has been wet and not properly dried, or carpet with years of accumulated organic material — produces musty odour, particularly when the home is warm and humid.

Signs:

• Musty smell in carpeted rooms that doesn't exist in hard-floor rooms
• Old carpet (more than 8–10 years)
• History of carpet getting wet from flooding, leaks or spills that weren't properly dried
• Smell worse in summer when heat activates organic compounds in the carpet

What to do: Professional carpet steam cleaning in Adelaide is the first step — hot water extraction removes much of the embedded organic matter that produces odour. If the smell returns quickly after cleaning, the carpet backing or underlay may have sustained mould damage that cleaning won't fix. Replacement may be needed.

4. Bathroom — Grout and Sealant

Mould in tile grout and silicone sealant in the bathroom is extremely common in Adelaide homes, particularly in bathrooms with inadequate ventilation. What looks like grey or black grout discolouration is often mould.

Signs:

• Musty smell concentrated in the bathroom
• Discoloured grout — grey, brown or black rather than white or cream
• Mould visible in the silicone sealant at the base of the shower, bath or basin

What to do: Scrub grout with a dedicated mould-killing grout cleaner or diluted bleach and a stiff brush. For silicone with embedded mould (where the mould doesn't scrub off cleanly), the sealant needs to be removed and replaced — you cannot clean mould out of the interior of a silicone bead, only off the surface. Improve bathroom ventilation: exhaust fan running during and 20 minutes after every shower.

5. Subfloor Moisture (Particularly in Older Homes)

Many older Adelaide homes — particularly pre-1980s construction — have a raised timber subfloor with a crawl space underneath. If this space has inadequate ventilation, or if rising damp is present, moisture accumulates and mould grows in the subfloor space. The MVOCs rise through floorboards and into the living space.

Signs:

• Musty smell that seems to come from the floor
• Older home with timber floors or floorboards over a raised subfloor
• Smell worse in winter (when subfloor moisture is typically highest in Adelaide's cooler, wetter months)
• Visible moisture or mould when you inspect the subfloor with a torch (access is usually via a removable panel outside)

What to do: Subfloor moisture is a specialist building issue. Solutions include improving subfloor ventilation (adding vents), installing a vapour barrier on the subfloor ground, or in severe cases, more extensive moisture management work. Engage a builder or specialist subfloor contractor.

6. Roof Cavity

A roof leak — even a minor one that isn't visibly dripping into the living space — can introduce moisture into the roof cavity that develops mould over time. The smell makes its way into the home through ceiling penetrations, light fittings and any gaps in the ceiling.

Signs:

• Musty smell that seems to come from above
• Smell concentrated in upper floors or areas under the roof
• Any history of roof issues or after heavy rain events

What to do: Roof inspection. If there's mould in the roof cavity, address the moisture source (the leak or inadequate ventilation) and then remediate the mould.

7. Drains

A slow or partially blocked drain can produce musty or sewage-adjacent smells. Organic matter accumulating in drain pipes produces microbial activity that generates odour.

Signs:

• Musty or sour smell from sink, shower or floor drain
• Smell that gets stronger when water is run
• Slow-draining fixture

What to do: Pour boiling water down the drain. Follow with a cup of baking soda and then a cup of white vinegar — the fizzing action helps dislodge organic buildup. Flush with more boiling water after 30 minutes. For persistent slow drains, a commercial drain cleaner or a plumber's snake to physically clear the blockage.

8. Stored Items — Books, Boxes, Fabrics

Old boxes, books, stored clothing and fabrics in a wardrobe, garage or spare room can develop mould from humidity over time and produce significant musty odour.

Signs:

• Musty smell concentrated in a storage area, wardrobe or spare room
• Books or paper with a damp, musty smell when you open them
• Fabric that smells when unfolded

What to do: Remove all items, air them outside in sunlight if possible. Discard anything that is visibly mouldy or smells strongly when handled. Wipe shelves and the storage space with a diluted white vinegar solution. Ensure good ventilation in storage areas — consider a small dehumidifier in persistently humid spaces.

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How to Find the Source of Your Musty Smell

If you can't immediately identify the source, a systematic approach helps:

1. Move from room to room with the smell as your guide. Where is it strongest?

2. Check concentration at floor and ceiling level. A stronger smell near the floor suggests carpet, subfloor or a wall at low level. Stronger near the ceiling suggests roof cavity or condensation above.

3. Open cupboards and wardrobes. Mould in enclosed spaces often produces concentrated odour that's immediately obvious when the door is opened.

4. Check behind and under appliances. The washing machine, the dishwasher, under the kitchen sink — plumbing leaks in these areas are common and produce mould that's not visible until you look.

5. Inspect bathroom grout and sealant closely with good light.

6. After rain: If the smell is worse after rain, water ingress or subfloor moisture is likely.

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What Never Works

Air freshener and candles: These mask smells temporarily. The source continues producing MVOCs and the smell returns.

Opening windows (alone): Ventilation dilutes the smell but doesn't eliminate the source. Necessary but not sufficient.

Cleaning surfaces around the source: If the mould is inside a wall, under carpet or in the subfloor, surface cleaning in the room won't touch it.

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For musty smells that come from cleaning-addressable sources — carpet, washing machines, bathroom mould, drains — a professional deep clean is an effective first step. A professional deep clean in Adelaide is an effective first step for cleaning-addressable sources — contact PF Cleaning and we'll give you an honest recommendation on whether cleaning will fix it or whether you need a building professional.

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If carpet is the source of your musty smell, see our guide on carpet cleaning vs vacuuming — including when steam cleaning is needed versus routine vacuuming.

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Written by Victor Jacon — Master Cleaner & Home Detailing Specialist, Founder of PF Cleaning Adelaide.