Mold, mildew and musty smells in carpet and couches

Because the smell sits where you cannot see it: in the cushion foam, the fabric backing, the underside of the base, or the wall and floor behind the couch. Old spills, sweat, pet hair and damp air collect there, and a couch against a cold wall or in a humid room stays damp enough to smell.

Take the cushions off, vacuum the seams and the underside, pull the couch away from the wall and run a fan and a dehumidifier, keeping the room's humidity low as the EPA's brief guide to mold and moisture advises. Check the tag under the cushions first: W means water-based cleaning, S means solvent only, W/S means either, and X means vacuum only (cleaning codes). If the smell is back once everything is dry, the cushions need a deep clean; spots or damp foam are a reason to read the mold sections below.

Air it, dry it and vacuum it. A closed, warm home gets stale and damp, and fabric absorbs that smell: open the windows, run fans for several hours, take the cushions off and stand them up, vacuum the couch and use baking soda on the fabric.

If the smell is still there after the air has changed and the couch is dry, a clean by extraction at your home helps; a couch is priced by its number of seats, see prices.

For carpet, run a fan and a dehumidifier until the air feels dry, lift a corner near the walls and windows to check that the pad is dry, vacuum slowly, then leave baking soda on the dry carpet overnight and vacuum again. If it still smells, it needs cleaning by extraction and a fast dry; if the pad is damp or you see growth, read the leak answer below.

Dry it fast: the EPA's brief guide to mold and moisture says to dry water-damaged items within 24–48 hours. Extract or blot out the water, dry both sides and the floor under it in moving air and shade, and do not put it back until the underside is dry; we clean rugs of every material except viscose, and a rug that stayed wet longer or has growth on the back may have to be replaced.

Take it outside or into a ventilated room, vacuum both sides, check the underside and the floor under it for dampness, and dry it flat in moving air in the shade. Sun fades dye, and a rug left on a damp floor smells again.

A rug that stays musty after it is dry needs cleaning. We clean rugs at your home on a drop cloth (see rug cleaning), and a rug that was wet for a long time may have growth on the back.

With gloves on, dab the spot with a damp white cloth: dirt is usually flat and sharp-edged and comes off on the cloth, while mold is fuzzy or powdery, spreads in irregular patches, often smells musty, sits where the cushion stayed damp and comes back after cleaning. A home test kit will not settle it.

Spots or patches that are fuzzy, powdery or slimy, white, gray, green, black or dark brown, usually on the underside, the seams or the back against a wall, along with a musty smell. Mildew starts as a flat, light powder that darkens as it spreads.

A dark patch with no smell may be dirt or a stain and not mold. If you are unsure, do not sniff it from close up; look at it in daylight and ask a specialist.

Not on its own: we clean furniture after mold, but cleaning is not a health treatment. Mold grows into the fabric, the foam and the frame of an upholstered piece, cleaning the surface does not reach what is inside, and wetting a cushion that is already damp adds moisture.

The EPA's advice is to fix the moisture first; a couch with mold through the fabric and padding is usually replaced, as the answer above says.

A light, surface mildew on a W-coded fabric can be brushed off outside, then the spot blotted with a little diluted white vinegar or detergent in cool water after a hidden-spot test, and dried quickly. Do not soak the cushion.

A mildew smell that returns after it dries means the damp is inside the cushion. At that point it is a moisture problem and not a surface one.

Yes. Carpet, the backing and the pad hold moisture and dirt, and mold can grow in them after a flood, a leak, a spill that stayed wet or a damp slab. Growth often starts on the underside, where you cannot see it.

How to prevent it: dry wet carpet, the pad and the floor under them within 24–48 hours, as the EPA's brief guide to mold and moisture advises, keep the humidity down and fix the leak.

Stop the leak and dry the carpet first; in an apartment, tell the landlord or manager in writing, with photos, right away. The carpet, the pad and the floor under them need to be dry within 24–48 hours, the EPA's window, which usually means lifting a corner, extracting the water and running fans and a dehumidifier.

If the carpet stayed wet longer than that, or there is growth on the back or the pad, the EPA says moldy carpet may have to be thrown away, and the pad goes with it. If the leak is fixed, the carpet is dry and the smell is only in the pile, cleaning by extraction takes out the dirt the smell lives in. We clean carpet after a leak or a flood once the water is stopped, and after mold; carpet is priced per room, see prices.

Start with your eyes, your nose and a damp check: lift a corner in a closet, look at the underside and the floor, and feel whether the pad is damp. If you see or smell mold, the EPA's advice is to deal with the moisture and the growth and not to rely on a test.

A mold specialist can inspect and take samples if you need a record, for example in a rental dispute. A home test kit does not tell you how much mold there is or where.

We make no health claim about mold; a question about a child's health is for a doctor, and about a dog's for a vet. The practical step is the same either way: keep children and pets off the area until the moisture is fixed and the carpet is dealt with, since the EPA's advice is to fix the water problem and clean up or remove the moldy material, and moldy carpet may have to be thrown away.

Leave an area larger than about 10 square feet to a specialist, and for a small one wear gloves, goggles and an N-95 respirator, as the EPA's brief guide says.

If the growth is on the carpet, the backing or the pad, in more than a small area, or the carpet stayed wet for days, then yes, the EPA says porous materials such as carpet may have to be thrown away if they become moldy. A carpet that smells musty after a spill and is now dry may be only dirty, and can be cleaned.

Replace the pad with the carpet, and fix the moisture first, or the new carpet will grow mold too.

A mold specialist finds where the moisture comes from, contains and removes the affected material and dries the area. That is a different job from cleaning, and the time to call one is when the area is large, the growth is on the pad or the subfloor, or the carpet was flooded.

We clean carpet after mold. The EPA's pages say what to ask a specialist.

• Carpet cleaning
• Rug cleaning
• Couch cleaning
• Prices

• Odors and smells: all guides
• Pet urine and accidents in carpet and rugs — Blot, flush with cool water, use an enzyme cleaner, and dry it fast; urine that reached the pad is the part a surface clean misses.
• How to deodorize a couch or rug — Find the source, pretreat it, flush it out and dry fast; enzymes break down organic matter, and a scent on its own covers a smell rather than removing it.
• Smoke and chemical smells in a couch — Cigarette and fire-pit smoke sits in fabric and comes out partly with ventilation and a deep clean; a new couch or carpet smell fades with fresh air; fire and wildfire damage is for a specialist.
• Dust mites, bed bugs and mold in a mattress — Dust mites are tiny and common in beds and are kept down by covers, hot washing and low humidity; bed bugs and mold need their own specialists.