A damp, musty smell in a home is usually caused by mould or mildew growing in areas with excess moisture. These microorganisms release gases called Microbial Volatile Organic Compounds (MVOCs), which create the characteristic odour.
The most common causes are condensation, poor ventilation, hidden leaks, and rising or penetrating damp. These issues are most often found in high-moisture areas such as basements, kitchens, and bathrooms.
That unmistakable musty smell — stale, earthy, and slightly sour — is one of the first signs that something is wrong with moisture levels in your home. Most people notice the smell long before they see any visible damp or mould, which actually makes it a useful early warning system.
This guide walks you through why damp smells develop, how to track down the source, and how to get rid of the smell permanently — rather than temporarily covering it up with an air freshener.
Why does damp smell the way it does?
The distinctive musty smell of a damp home is caused by microbial volatile organic compounds (MVOCs) — gases released by mould and mildew as they grow and break down organic materials. You’re essentially smelling mould activity, often before any visible colonies appear on walls or ceilings.
Mould can begin producing these compounds within 24–48 hours of the right moisture conditions being established, which is why a damp smell can seem to appear out of nowhere after a bout of wet weather or a period of poor ventilation.
Expert Tip: If you can smell damp but can’t see any visible mould, don’t assume the problem is minor. Hidden mould commonly grows inside wall cavities, behind plasterboard, under carpets, inside wardrobes against external walls, and beneath kitchen and bathroom units. The smell may be the only early warning you get.
Where is the damp smell coming from? Common sources
Before you can treat the smell, you need to identify its source. In London homes — which tend to be older, densely occupied, and often poorly ventilated — there are several usual suspects.
Condensation and mould growth
The most common cause in UK homes. When warm, moisture-laden air meets cold surfaces, water condenses. Over time, mould develops on walls, window reveals, behind furniture, and inside wardrobes. The smell tends to be worse in winter and in rooms with poor ventilation such as bedrooms and bathrooms.
Where to look: Behind wardrobes on external walls, in the corners of rooms, around window frames, and on the ceilings of poorly ventilated rooms.
Rising damp
Ground moisture travelling up through the masonry can cause a persistent damp smell at low level — around skirting boards, in the base of walls, and under staircases. Rising damp has a particularly distinct earthy, “old house” smell due to the salt deposits it carries.
Where to look: Lower sections of walls, behind radiators at floor level, and under the stairs.
Penetrating damp
Water entering through a defective external wall, roof, or chimney can cause damp patches and smell deep inside the structure. This can affect any level of a property and often has a stronger, more acute smell after heavy rain.
Where to look: Areas beneath a flat roof, around chimney breasts, and on walls adjacent to blocked or overflowing gutters.
Damp under floors
Suspended timber floors with poor sub-floor ventilation are common in London’s Victorian housing stock. If the void beneath the floor stays damp, the smell can permeate up through the floorboards and into rooms. This is often mistaken for damp walls.
Where to look: Lift a corner of carpet near an external wall and smell the floorboards beneath. Check air bricks on the external walls for blockages.
Damp in drains or plumbing
A musty or damp smell that seems to come and go, particularly in kitchens and bathrooms, can sometimes be a slow drain, a dry trap in an infrequently used sink, or condensation on cold pipework.
Where to look: Run water in infrequently used sinks to refill traps. Check underneath sinks and baths for any signs of slow leaks.
How to get rid of a damp smell: step by step
Step 1: Locate and fix the moisture source
This is the only permanent solution. Deodorisers, activated charcoal, and air fresheners will not eliminate a damp smell — they will mask it temporarily. Until the source of moisture is removed, the smell will return. Use the checklist above to narrow down where the moisture is entering or accumulating.
Step 2: Dry the affected area thoroughly
Once the source is addressed, the affected area needs to dry out. Open windows on dry days, increase background heating, and use a dehumidifier to draw excess moisture from the air and fabric of the building. Be patient — solid brick walls can take weeks or even months to dry fully.
Expert Tip: A domestic dehumidifier can process 10–20 litres of water per day in a damp room. Empty the tank daily and keep doors to the rest of the house closed while it runs, so it’s working on the affected area rather than the whole house.
👉 Read our guide on how to treat damp walls →
Step 3: Remove mould-affected materials where necessary
Mould growing on painted walls or tiles can be treated with a specialist mould remover. However, mould that has penetrated plaster, grout, sealant, or soft furnishings cannot be fully removed — those materials will need to be replaced. Continuing to smell damp after cleaning a visible patch of mould usually means mould is still present inside the material.
Step 4: Clean and deodorise
Once the area is dry and mould-free, the smell should reduce significantly. To speed up the process:
- Wash all soft furnishings, curtains, and bedding at the highest temperature the fabric allows
- Sprinkle bicarbonate of soda on carpets and upholstery, leave for several hours, and vacuum thoroughly
- Place bowls of white vinegar in the affected room for 24–48 hours (this neutralises odour compounds without adding fragrance)
- Replace any air bricks, extractor fans, or trickle vents that are blocked or damaged
Step 5: Improve ventilation to prevent recurrence
Poor ventilation is the single biggest driver of condensation damp smell in London homes. Practical steps include:
- Running bathroom and kitchen extractor fans during and for 20–30 minutes after use
- Using trickle vents in window frames rather than keeping windows fully closed
- Moving furniture slightly away from external walls to allow air circulation
- Considering a Positive Input Ventilation (PIV) unit if condensation is a persistent problem
Expert Tip: In flats — particularly those on higher floors or with east-facing walls — condensation is nearly always the primary driver of damp smells. A PIV system can transform indoor air quality and permanently solve condensation-related mould and smell problems for a fraction of the cost of replastering and redecorating.
👉 View our Positive Input Ventilation services →
When a damp smell means calling in a professional
Some damp smells signal problems that go beyond what can be self-diagnosed or self-treated:
- The smell persists after thorough drying and cleaning
- You can’t find a visible source after checking all the likely areas
- The smell is worse after heavy rain (suggests penetrating damp)
- The smell is strongest at floor level near external walls (suggests rising damp)
- There is a persistent smell even in a well-ventilated room
In these cases, a professional damp survey is the most reliable next step. A surveyor will use moisture meters, thermal imaging, and experience with London’s housing stock to identify exactly what is causing the problem — and give you a clear treatment plan.
👉 Book a professional damp survey in London →
Products that help — and ones that don’t
Worth trying:
- Dehumidifiers — genuinely effective at reducing moisture levels and accelerating drying
- Mould-resistant paint — appropriate for kitchens and bathrooms as a preventative, but not a cure
- Bicarbonate of soda — a natural odour absorber, useful during the drying-out phase
- Extractor fans with humidity sensors — automatically activate when moisture levels rise
Don’t bother:
- Plug-in air fresheners — mask the smell but do nothing for the underlying damp
- Paint-on damp sealers (DIY) — often trap moisture rather than stopping it
- Moisture-absorbing crystals alone — useful supplementary products but far too low-capacity to treat a genuine damp problem
Frequently Asked Questions
Why does my house smell damp but I can’t see any mould?
A damp smell without visible mould usually means hidden mould is present. It often grows behind plasterboard, inside walls, under carpets, or inside wardrobes. The odour appears before visible growth. A professional damp survey using a damp meter and thermal imaging is the most reliable way to find it.
Does a damp smell mean black mould?
No, a damp smell does not always mean black mould. The musty odour is produced by many types of mould and mildew, often grey, green, or white. Black mould (Stachybotrys chartarum) is just one species and produces the same type of smell as others.
How long does it take for a damp smell to go after fixing the problem?
A damp smell can take days to several weeks to disappear after fixing the source. Light condensation issues may clear within days, while damp in solid walls can take 4 to 12 weeks to dry. Using a dehumidifier helps speed up the process.
Can damp smell affect your health?
Yes, damp smells can affect your health. The gases released by mould can irritate airways, trigger asthma, and cause headaches or fatigue. Children, the elderly, and people with respiratory conditions are most at risk. Persistent damp smells should be treated as a health concern.
Why does my wardrobe smell damp even though the walls look fine?
A wardrobe can smell damp because mould forms behind it on cold external walls. These areas lack airflow and warmth, creating condensation. This hidden space is often the first place mould develops. Moving the wardrobe and checking behind it usually reveals the issue.
Will painting over damp walls get rid of the smell?
No, painting over damp walls will not remove the smell. It only hides the problem temporarily. The moisture and mould will return and break through the paint. The correct solution is to fix the moisture source and treat or replace affected materials.
👉 Read our guide: Why is there mould in my wardrobe? →
Can’t find the source of your damp smell?
If you’ve checked everywhere and the smell persists, our team of damp specialists can identify the cause quickly using professional moisture meters and thermal imaging. We cover all of London and North Hertfordshire.
Book a damp survey → | Call us: 020 4542 6114
We provide damp surveys and treatment across London boroughs including Barnet, Haringey, Hackney, Camden, Kensington, Ealing, and beyond.