Musty smell in your house: find the source and get rid of it
Last reviewed · Not medical advice
A musty smell is mold or mildew growing somewhere damp. Indoor humidity above about 60% is the usual cause; the rest are a specific wet spot like a leak, basement, crawlspace, or AC drain. Air fresheners won't fix it. Find the moisture, dry it out, and clean or replace what grew mildew. Start with an inexpensive hygrometer: if humidity is over 60%, dehumidify first. If it's normal, the source is local and you can sniff it out room by room.
Most likely causes
Ranked for this situation. Open any cause for checks and fixes.
- 1
Indoor humidity too high
most commonIf the smell is everywhere but faint, and worse in summer or when the house is shut, humidity is the first suspect.
Points to this:- Smell everywhere, worse in humid weather or when the house is closed up
- Condensation on windows; clammy air; towels that never dry
Check it, fix it, who to call
Safe checks- Put a hygrometer (an inexpensive humidity gauge) in the smelly area for 24 hours.
- EPA guidance: keep indoor humidity below 60%, ideally 30–50%.
Fix- Run a dehumidifier, and AC in summer.
- Use bathroom and kitchen exhaust fans; vent the dryer outdoors.
- Wash or dry-clean fabrics that picked up the smell.
DIY stops here: If you can't get below 60% with a dehumidifier, find the moisture source (basement, crawlspace, leaks).
Who fixes it: You (DIY)
More on this - 2
Damp basement or foundation seepage
most commonWithin daysIn homes with basements, the smell often starts downstairs and rises through the house.
Points to this:- Musty smell starts in the basement and drifts upstairs
- White chalky deposits (efflorescence), damp spots, or water lines on walls
- Worse after rain or in humid months
Check it, fix it, who to call
Safe checks- Tape a 1-foot square of plastic sheet to the wall or floor for 48 hours. Moisture under it means water is coming through the concrete; moisture on top means humid air is condensing on it.
- Check that gutters and downspouts discharge well away from the foundation.
Fix- Fix grading and gutters first — it's cheap and often enough.
- Run a basement dehumidifier.
- Get stored items off the floor and out of cardboard.
DIY stops here: Active seepage or standing water needs a waterproofing contractor.
Who fixes it: Basement waterproofing contractor
More on this - 3
Damp crawlspace
commonWithin daysIn crawlspace homes, damp crawlspace air is pulled up through the floor.
Points to this:- House is on a crawlspace; smell is strongest at floor level or near floor registers
- Worse in summer and after rain
Check it, fix it, who to call
Safe checks- From the access hatch, look for standing water, bare dirt with no vapor barrier, or sagging insulation (don't crawl in if there's standing water or animal activity).
Fix- Ground vapor barrier, drainage, and in many cases encapsulation with a dehumidifier.
- Seal ductwork in the crawlspace.
DIY stops here: Encapsulation and drainage are contractor work.
Who fixes it: Basement waterproofing contractor
More on this - 4
AC evaporator coil or condensate drain
commonWithin daysIf the smell comes out of the vents when the AC runs, start with the AC — see the AC page.
Points to this:- Smell comes out of vents when the AC starts, then may fade
- Water around the indoor unit, or a drain line that never drips outside
Check it, fix it, who to call
Safe checks- Smell a supply vent right as the AC kicks on.
- Check the condensate line outlet outside or at the pump — it should drip while cooling.
- Replace the air filter.
Fix- Clear the condensate line (many have a cleanout tee you can flush).
- An HVAC tech cleans the coil and pan.
DIY stops here: Coil cleaning means opening the air handler — HVAC tech.
Who fixes it: HVAC technician
More on this - 5
Hidden water leak
commonWithin daysA localized smell near a bathroom, kitchen, or wall points here.
Points to this:- Smell strongest at one wall, ceiling patch, or cabinet
- Stains, bubbling paint, warped trim, or soft flooring
- Water bill crept up, or the meter moves with everything off
Check it, fix it, who to call
Safe checks- Open sink base cabinets and look and feel for damp wood.
- Turn off all water and watch the meter for 30 minutes — movement means a leak.
- Sniff along baseboards near bathrooms, kitchens, and exterior walls.
Fix- Stop the leak first.
- Dry or remove wet materials; drywall that stayed wet for days usually has to be cut out.
DIY stops here: Opening walls is fine for small areas. Large or long-running leaks need a water-damage pro with moisture meters.
Who fixes it: Water damage / restoration company
More on this - 6
Mold or mildew growing on surfaces
commonWithin daysVisible growth on drywall, grout, window frames, ceilings, or stored items is both the source and the evidence.
Points to this:- Black, green, white, or gray speckled growth
- Growth near a moisture source
Check it, fix it, who to call
Safe checks- Measure the affected area.
- Under about 10 square feet (roughly 3 ft × 3 ft), EPA guidance says most homeowners can clean it themselves.
Fix- Fix the moisture first.
- Scrub hard surfaces with detergent and water, and dry completely (EPA).
- Porous materials like ceiling tiles and carpet that have gone moldy may have to be thrown away.
DIY stops here: More than about 10 sq ft, mold after significant water damage, or mold you suspect is in the HVAC system: bring in a professional.
Who fixes it: Mold remediation company
More on this - 7
Carpet or pad that got wet
less commonWithin daysA spill, pet accident, leak, or wet carpet cleaning can soak the pad. The surface dries but the pad stays damp and goes musty.
Points to this:- Smell strongest at floor level in one area
- Worse on humid days or after carpet cleaning
Check it, fix it, who to call
Safe checks- Press a dry paper towel hard into the carpet — dampness shows up.
- Lift a corner at the tack strip and check the pad and subfloor.
Fix- Dry the area fully with fans and a dehumidifier.
- Replace pad that stayed wet more than a day or two, or that is stained.
DIY stops here: Large areas or any sewage-contaminated carpet go to a restoration company.
Who fixes it: Water damage / restoration company
More on this - 8
Front-load washer gasket or drum
less commonIf it's mostly the laundry room and the clothes.
Points to this:- Clothes smell musty right out of the washer
- Dark residue in the folds of the door gasket
Check it, fix it, who to call
Safe checks- Pull back the gasket folds and look; smell the detergent drawer.
Fix- Clean the gasket and drawer; run the washer's cleaning cycle.
- Leave the door and drawer open between loads.
DIY stops here: Persistent smell after cleaning can be a slow drain or the drain pump — appliance repair.
Who fixes it: Appliance repair
More on this - 9
Stored items that absorbed dampness
less commonCardboard, old books, upholstered furniture, and boxed clothing soak up humidity and hold onto mildew odor long after the air dries.
Points to this:- Smell is strongest near storage
- Old furniture or books smell musty up close
Check it, fix it, who to call
Safe checks- Move suspect items out of the room for a few days and see if the room improves.
Fix- Move storage into plastic bins, off the floor.
- Air out, clean, or discard items that keep smelling.
DIY stops here: None — this is a sorting job.
Who fixes it: You (DIY)
More on this
How we rank causes: by how often each one explains this smell in ordinary homes, according to plumbing, HVAC, electrical, and building-science guidance, adjusted for the context on this page. The labels are judgments, not measured statistics. Anything dangerous that can't be ruled out (gas, fire, electrical) is covered in the safety box at the top of the page, whatever its rank.
Which one is it?
| What you notice | Most likely source | Go to |
|---|---|---|
| Faint everywhere, worse on humid days | Humidity over 60% | Hygrometer + dehumidifier |
| Strongest in the basement or downstairs | Basement moisture | Basement page |
| Strongest near floor registers, no basement | Crawlspace | Check the crawlspace |
| Blows out of vents when AC starts | AC coil or drain | AC page |
| One room or one wall | Leak, closet, carpet | Musty room page |
| Musty but you can't see any mold | Hidden moisture | No-visible-mold page |
| Clothes smell musty after washing | Washer gasket | Clean the washer |
Narrow it down
Answer in order. Stop at the first yes.
- 1Is indoor humidity over 60% (measured, not guessed)?Yes → Dehumidify to 30–50% for a week. If the smell fades, that was it. Then find out why the house runs damp.No → The source is local. Keep going.
- 2Is it strongest at the vents, and only when the HVAC runs?Yes → It's the AC coil, the drain, or the ducts. Go thereNo → Keep going.
- 3Is it strongest in the basement or on the lowest floor?Yes → It's basement moisture. Go thereNo → Keep going.
- 4Is it concentrated in one room?Yes → Work that room systematically. Go thereNo → Keep going.
- 5No visible mold anywhere, humidity normal, still musty?Yes → Look for hidden moisture. Go there
Safe checks you can do yourself
In the order that finds the source fastest.
- 1
Measure humidity (24 hours)
Put a digital hygrometer on the main floor, and another in the basement if you have one. EPA guidance is to keep indoor humidity below 60%, ideally 30–50%.
- 2
Do a sniff walk
Go outside for 10 minutes to reset your nose, then walk in and go room by room, top to bottom. Note where the smell is strongest. Open closets and sink cabinets, and smell at floor level.
- 3
Check the usual wet spots
Look under every sink, behind the toilets, around the water heater, the washer, and window sills, and along the base of exterior walls. You're looking for stains, damp wood, bubbling paint, and dark spotting.
- 4
Run the HVAC test
Smell a supply vent right as the AC or heat starts, then again after 10 minutes. A burst of musty air at start-up points at the coil, the drain, or the ducts.
- 5
Check the lowest level
Basement: look for damp walls, white mineral deposits, and cardboard on the floor. Crawlspace: look in from the hatch for standing water or a missing vapor barrier.
How to get rid of a musty smell for good
Odor products don't solve this. Musty smell is a by-product of something growing on a damp surface, so it comes back until the surface stays dry. The order that works:
1. Stop the water: fix the leak, the gutter, the AC drain, or the missing vapor barrier. 2. Dry the air: run a dehumidifier to bring humidity to 30–50% and keep it there. 3. Clean or remove what grew: EPA guidance says to scrub hard surfaces with detergent and water and dry them completely; porous materials like carpet pad, ceiling tiles, and cardboard that went moldy usually have to go. 4. Then deodorize what's left: wash fabrics, air out furniture, and change the HVAC filter.
If you do steps 3 and 4 without 1 and 2, the smell is usually back within weeks.
Is a musty smell always mold?
Usually it's mold or mildew. Mildew is the everyday name for surface mold on damp fabrics and grout. Sometimes it's simply damp: wet concrete, wet cardboard, a wet carpet pad. Either way it points to moisture. For visible growth, EPA says testing is usually unnecessary: if you can see it, deal with it and the moisture behind it.
When DIY stops
- Visible mold larger than about 10 square feet (roughly 3 × 3 ft) — EPA guidance points you to a professional.
- Mold after a major leak or flood, or drywall that stayed wet for days.
- You suspect mold inside the HVAC system. EPA advises not running it until it's dealt with.
- Water coming through foundation walls or standing in the crawlspace.
Who to call
- Water damage / restoration company
You found a leak and materials are wet. They dry the structure and measure moisture behind walls.
Finds wet materials with moisture meters and dries structures out.
- Mold remediation company
Visible growth over about 10 sq ft, or mold behind walls.
Contains and removes mold growth too large or too hidden to handle yourself.
- HVAC technician
The smell comes from the vents or the air handler.
Furnaces, air conditioners, coils, condensate drains, blowers, and ducts.
- Basement waterproofing contractor
The basement or crawlspace takes on water.
Foundation seepage, drainage, sump systems, and crawlspace encapsulation.
- Home inspector
You've done the checks and still can't localize it.
A whole-house look when you can't localize a problem.
Answer a few questions about where and when you smell it. You'll get the causes ranked for your situation.
Frequently asked questions
Why does my house suddenly smell musty?
Something changed the moisture balance: a stretch of humid weather, a new leak, a clogged AC drain, or the house being closed up for a trip or a season. Measure humidity first, then check for anything that got wet recently.
Can a dehumidifier get rid of a musty smell?
Often, yes — if humidity is the cause. It won't fix a leak or remove mold that's already growing. If humidity is under 60% and it still smells, look for a local source.
Do air purifiers or air fresheners help?
They can reduce the smell in the air for a while, but they don't touch the source. The smell returns when you stop.
Should I test for mold?
EPA's guidance: if mold is visible, sampling is usually unnecessary. Testing makes more sense when there's a strong musty smell and no visible growth, and even then, finding the moisture matters more.
Who do I call for a musty smell in my house?
It depends on the source: a plumber or water-damage company for leaks, an HVAC tech for vents and AC, a waterproofing contractor for basements and crawlspaces, and mold remediation for large or hidden growth. If you can't pin it down, a home inspector can do a whole-house look.
Related smells
Sources
- A Brief Guide to Mold, Moisture and Your Home — U.S. EPA
- Mold Cleanup in Your Home — U.S. EPA