Musty Smell in Basement? Causes and How to Get Rid of It

Short answer: A musty smell in the basement almost always means moisture and mold or mildew. To get rid of it, find and fix the moisture source, bring humidity down to 30 to 50 percent with a dehumidifier, and clean or remove anything moldy. Covering the odor won't work, because the smell returns as long as the moisture does.

That earthy, damp-cardboard smell is one of the most common reasons Laurel homeowners call us. It's easy to ignore, but it's your basement telling you something is wet. If you find mold spread over more than a small area, Laurel Dry Pros provides mold remediation in Laurel. Here's how to track down the cause and fix it.

This is general information, not medical advice. If someone in your home has health concerns, talk with a doctor.

What causes a musty smell in the basement?

The smell comes from gases released by mold and mildew as they grow. They need moisture to grow, so the real question is: where is the water coming from?

Cause	Where to look	What helps
High humidity	Whole basement, worse in summer	Dehumidifier set to 30 to 50 percent
Ground water seepage	Wall-floor joint, foundation cracks, white chalky deposits	Grading, gutters, crack sealing, drainage
Slow plumbing leak	Under sinks, around the water heater, washer, ceiling below a bathroom	Fix the leak, dry the area
Past flood not fully dried	Under carpet, behind paneling, inside walls	Remove wet materials, dry, remediate
Sump pit	Open pit, damp around the basin	Sealed lid, working pump. See our sump pump guide
Condensation	Cold water pipes, ducts and walls in summer	Insulate pipes, lower humidity
Dirty or wet carpet	Carpet over concrete	Remove carpet and pad if they stay damp
Crawl space	Area next to the basement	Vapor barrier and drying

How to find the source of the smell

Follow your nose. Walk the basement slowly. The smell is strongest near the source.
Check low and hidden spots. Look under stairs, in closets, behind boxes, behind paneling and under carpet edges.
Look for clues. Water stains, white chalky deposits on concrete (called efflorescence), peeling paint, rust on metal and warped wood all point to moisture.
Measure humidity. A cheap hygrometer shows the room's humidity. Above 60 percent is a problem.
Use a moisture meter. Check drywall and wood near the floor and outside walls.
Check after rain. If the smell gets worse after storms, ground water is likely.

Can't find the source of a musty smell? Call (301) 368-0221 and we'll check with moisture meters and a thermal camera.

Call (301) 368-0221

How to get rid of a musty smell in the basement

1. Fix the moisture

Nothing else works until the water stops. Fix leaks. Clean gutters and extend downspouts. Make sure the ground slopes away from the house. Seal foundation cracks.

2. Lower the humidity

The EPA recommends indoor humidity below 60 percent, ideally between 30 and 50 percent. Run a dehumidifier sized for the space, and set it to drain to the sump or a floor drain so you don't have to empty it. Keep windows closed on humid summer days.

3. Clean or remove moldy materials

For small areas under about 10 square feet on hard surfaces, the EPA says you can scrub with detergent and water while wearing an N-95 respirator, gloves and goggles. Throw out porous items that have mold, such as cardboard boxes, ceiling tiles and old carpet pad. Larger areas or mold inside walls need a professional.

4. Improve airflow

Move boxes away from walls. Use plastic bins instead of cardboard. Leave closet doors open. Make sure dryer vents go outside.

5. Clean what's left

Wash hard surfaces, launder fabrics and vacuum with a HEPA vacuum to remove spores and dust.

Musty smell vs. sewer smell

A musty smell is earthy and damp. A rotten-egg or sewage smell is different. It often means a dry floor drain trap, a cracked sewer pipe or a sewer backup. Pour water into unused floor drains to refill the trap. If you see waste or water coming up a drain, read our guide to sewage backup cleanup.

How to prevent a musty basement

Run a dehumidifier from late spring through early fall.
Check humidity monthly with a hygrometer.
Store items in plastic bins, off the floor.
Avoid carpet in basements that get damp. Use tile or vinyl.
Test the sump pump twice a year.
Fix plumbing leaks right away.
Keep gutters and downspouts clear.
Dry any spill or leak within 24 to 48 hours.

Local note: Older basements in Silver Spring and the lower levels of split-level homes in Beltsville are common sources of musty-smell calls. Crawl spaces under Beltsville homes can send odors up into living areas. Finished basements in Columbia with carpet over concrete often stay damp.

Related reading: See how long it takes mold to grow after a leak, and what to do right away when your basement floods.

When should you call a mold professional?

Call a pro when the smell doesn't go away after you lower humidity, when you see mold over more than about 10 square feet, when you think mold is inside walls or behind paneling, or after a flood or sewer backup.

Musty basement in Laurel? Call (301) 368-0221 to reach Laurel Dry Pros. We'll find the moisture and remove the mold.

Frequently asked questions

Why does my basement smell musty?

A musty smell usually means mold or mildew is growing somewhere, fed by moisture. The moisture can come from high humidity, a slow leak, ground water seeping through walls, or a past flood that wasn't fully dried.

Is a musty smell in the basement dangerous?

The smell itself is a warning sign, not the problem. It means mold may be growing. Mold can trigger allergy and asthma symptoms in some people, so find and fix the source.

Will a dehumidifier get rid of the musty smell?

It helps if humidity is the main cause. A dehumidifier that keeps the basement between 30 and 50 percent humidity can stop new mold. It won't remove mold that's already growing, so moldy materials still need cleaning or removal.

How do I find the source of a musty smell?

Follow your nose to where it's strongest. Check under carpet, behind paneling, in closets, around the sump pit, under stairs and near the water heater. A moisture meter or thermal camera can find damp spots you can't see.

Do air fresheners or vinegar fix a musty smell?

They can cover it for a while. They don't fix the moisture or remove the mold, so the smell comes back.

Sources

About this article. Written by Laurel Dry Pros Editorial and checked against the sources listed above. Last updated November 1, 2026. General information, not legal, insurance or professional advice. Read our editorial policy and disclaimer.