How to get rid of mildew smell (musty, moldy or sour)

Step by step

1. 1

   Find where the damp comes from

   Look for the moisture source: a leak, condensation, high humidity, a damp closet, wet laundry left in the washer, or a towel that never dries. A musty smell with no visible mold points to hidden growth behind walls, under carpet or in ducts.

   Why: Mold and odor bacteria only grow where moisture lingers. If the damp stays, the smell comes back however well you clean.

2. 2

   Brush off loose mildew outdoors

   Take mildewed fabrics, shoes or cushions outside and brush or shake off the surface growth. Vacuum upholstery and dispose of the vacuum bag afterward.

   Why: Doing it outdoors keeps spores from spreading through the house.

3. 3

   Wash fabrics hot with bleach where safe

   Pretreat dark spots with heavy-duty liquid detergent, then wash in the hottest water the care label allows with heavy-duty detergent and chlorine bleach if the fabric can take it. Otherwise soak in oxygen bleach and hot water for at least 30 minutes, then wash.

   Why: Detergent removes the growth and the body oils and soil it feeds on. Bleach oxidizes the mold, its stains and odor-making organisms.

4. 4

   Clean hard surfaces with detergent and water

   Scrub mold off walls, tile and other hard surfaces with detergent and water, then dry completely. Wear an N-95 respirator, gloves and goggles without vent holes.

   Why: Killing mold isn't enough. Dead mold still causes allergic reactions and still has to be physically removed.

5. 5

   Dry everything within 24 to 48 hours

   Dry washed items fully and promptly, in sun and moving air where possible. Run fans, exhaust fans or a dehumidifier in damp rooms.

   Why: Mold won't grow on materials dried within 24 to 48 hours in most cases.

6. 6

   Keep humidity down

   Aim for indoor relative humidity below 60%, ideally 30 to 50%. Don't put damp clothes or towels in a hamper, and leave closet doors open to air.

   Why: Low humidity stops new growth, which is the only way to keep the smell from returning.

What causes a musty or mildew smell

Mildew is mold growing on a damp surface. As it grows it gives off microbial volatile organic compounds (mVOCs), and those are what you smell as musty or moldy. It thrives in warm, moist air, on damp clothing, in bathrooms and on the dirt, greasy film and soap scum it can feed on.

The sour smell of towels or laundry that dried slowly is usually bacteria rather than mold. Researchers traced much of it to Moraxella osloensis, which survives washing and drying and makes a compound called 4-methyl-3-hexenoic acid while the fibers stay wet. It's described as smelling like a wet, dirty dishcloth. The trigger is the same in both cases: moisture that hangs around.

Why sprays and fresheners don't work

A musty smell means something is actively growing and producing odor. Fragrance covers that for a short while, and then the smell returns. EPA treats a moldy odor as a reason to look for mold, and says cleanup isn't finished until the moisture problem is fixed and the visible mold and moldy odor are gone.

The mildew stain guide covers the black or brown spots mildew leaves on fabric and surfaces.

Mildew smell by place

Clothes: hot wash with bleach where safe, several times if needed. See mildew smell in clothes.

Towels: sour towels need a hot wash and fast, complete drying. See mildew smell in towels.

A house or basement: the smell points to moisture and possibly hidden mold. See musty smell in a house.

Carpet or a car: dry wet carpet and padding fast, find and fix the leak, and replace padding that stays moldy.

Shoes: keep them clean and dry. For mildewed leather, wipe with equal parts denatured alcohol and water after a colorfastness test and dry in moving air. If mildew remains, wash quickly with thick suds of mild soap or saddle soap, wipe with a damp cloth, air-dry and polish.

By situation

Musty smell but no visible mold

Suspect hidden mold: behind drywall, wallpaper or paneling, on the top of ceiling tiles, under carpet and padding, or inside ductwork. Find and fix the moisture, and get help for anything larger than about 10 square feet.

Sour smell after washing

This is usually bacterial, from laundry that sat wet or dried slowly. Rewash with enough detergent in the warmest water the fabric allows, then dry it completely right away.

Stored clothes and linens smell musty

Wash in warm water with enough detergent. If the smell lingers, soak in baking soda and water, then wash again. Keep open containers of baking soda or activated charcoal in the closet and lower the humidity.

Mattresses, upholstery and rugs

Vacuum or brush off the mildew, then dry and air the item in the sun for several hours. If mildew remains, sponge lightly with 1 cup rubbing or denatured alcohol mixed with 1 cup water, after a colorfastness test, and dry thoroughly.

Silk, wool and stretch fabrics

Skip chlorine bleach, which damages silk, wool and spandex. Use an oxygen bleach soak for washable items, or take them to a dry cleaner.

What not to do

• Don't spray air freshener over a musty smell. The smell signals mold growth that's still going. Covering it lets the growth spread.
• Don't leave damp clothes or towels in a pile or hamper. Mildew and odor bacteria grow quickly on damp, warm textiles.
• Don't rely on killing mold instead of removing it. Dead mold can still trigger allergies, so it has to be cleaned off.
• Don't mix chlorine bleach with ammonia or other cleaners. The combination releases toxic chloramine gas.

Other methods that work

Chlorine bleach spot treatment

For bleach-safe fabrics, sponge on or soak in 2 tablespoons of liquid chlorine bleach per quart of water for 5 to 15 minutes, then rinse. For a full load, add 1 cup of chlorine bleach to the washer.

Caution: Ventilate, test colorfastness first, and keep it off silk, wool and spandex.

Oxygen bleach soak

For colors and fabrics that can't take chlorine, soak in oxygen bleach for 30 minutes or longer, overnight for old stains, then rinse and wash.

Caution: Check the care label; oxygen bleach isn't safe for every fiber either.

Sun and fresh air

Several hours of sun and moving air dry out mildew on mattresses, cushions and rugs.

Caution: Sun alone may not kill the bacteria behind sour laundry, which tolerate drying and UV light. Wash first.

Stain still there?

The smell returns after a day or two

The moisture source is still there, or growth is hidden. Check humidity, look for leaks, and make sure items are fully dry before storing them.

Clothes still smell musty after one wash

Mildew may take several washes. Repeat with hot water and bleach where safe, and dry fully between rounds.

Carpet smells musty after it got wet

If the moisture is in the padding or the floor underneath, surface cleaning won't hold. Lift the carpet, fix the moisture source, and replace padding that stays moldy.

Safety

• Wear an N-95 respirator, gloves and non-vented goggles when cleaning visible mold, and don't touch it with bare hands.
• Mildew is believed to contribute to asthma and other breathing problems, especially in children. Exposure to mVOCs has been linked to headaches, nasal irritation, dizziness and nausea.
• Ventilate when using chlorine bleach and never mix it with ammonia or acids.

Never mix cleaning products; see chemicals you must never combine.

Questions

Get rid of mildew in a specific place

• Mildew in a basement
• Mildew in a car
• Mildew in carpet
• Mildew in clothes
• Mildew in the house
• Mildew in towels
• Mildew in a washing machine