Where the Smell Comes From and How to Remove It

Mould smell — that musty, earthy odour — comes from volatile organic compounds that mould releases as it grows and breaks down organic material. The smell lingers even after you've cleaned visible mould because it's trapped in porous surfaces like drywall, carpet, wood, and insulation. To remove it, you need to address both the mould itself and the materials that have absorbed the odour.

The fastest way is to open windows and run fans to move air out of the space while you work. But ventilation alone won't eliminate the smell if mould is still present or if porous materials are saturated. You'll need to clean the mould, replace heavily affected materials, and then treat the remaining odour with absorbents or neutralizers.

Key Takeaways

  • Mould smell comes from gases the mould releases, not just from visible growth, so cleaning surfaces alone may not remove the odour completely.
  • Porous materials like drywall, carpet, and insulation absorb and hold mould smell; if they're heavily affected, replacing them is faster than trying to neutralize the odour.
  • Baking soda, activated charcoal, and white vinegar absorb or neutralize mould smell in rooms and inside materials like walls.
  • Continuous air circulation with open windows and fans removes mould smell faster than any chemical treatment.
  • If the smell returns after cleaning, mould is still growing somewhere — check hidden areas like inside walls, under flooring, and around pipes.

Clean or Remove the Mould First

You cannot smell your way to a mould-free room. If you treat the odour without removing the mould, the smell will return within days or weeks because the mould keeps producing it. Start by finding and cleaning all visible mould, then address hidden growth in walls, under flooring, and around pipes.

For surface mould on hard materials like tile or painted wood, scrub with a stiff brush and a solution of one part white vinegar to one part water, or use a commercial mould cleaner. Let it sit for 10 to 15 minutes before scrubbing. For porous materials like drywall or carpet that show mould growth, the material usually needs to be removed and replaced — cleaning alone won't stop the mould from growing back into the material and continuing to produce smell.

If you find mould in walls, under flooring, or in insulation, you may need a professional assessment. Mould in hidden spaces can be extensive and difficult to reach, and disturbing it without proper containment can spread spores throughout your home. A mould removal specialist can determine whether the affected area can be cleaned or needs to be cut out and replaced.

Use Baking Soda to Absorb Odour in Rooms

Baking soda absorbs mould smell from the air and from soft materials. Spread it on carpets, upholstered furniture, and mattresses where mould smell is trapped. Leave it for 24 to 48 hours, then vacuum thoroughly. For a stronger effect, mix baking soda with a few drops of essential oil like lavender or lemon before spreading it.

In rooms with lingering smell, place open bowls of baking soda in corners and under furniture. Replace the baking soda every two to three days until the smell is gone. This method works best in small, enclosed spaces like closets or bathrooms. In larger rooms, baking soda will help but won't eliminate the smell on its own — you'll need ventilation and air circulation as well.

set up Charcoal and Other Absorbents

Activated charcoal absorbs mould smell more effectively than baking soda because it has a larger surface area. Place activated charcoal in mesh bags or open containers around the room, especially in corners, closets, and under furniture where air moves slowly. Replace it every one to two weeks until the smell is gone.

Other absorbents that work include crumpled newspaper, coffee grounds, and cat litter (unscented). None of these are as effective as activated charcoal or baking soda, but they're useful if you have them on hand. Avoid scented products like air fresheners or scented candles — they mask the smell rather than remove it, and the smell returns once the scent fades.

Ventilate Continuously Until the Smell Is Gone

Open windows on opposite sides of the room to create cross-ventilation. Run box fans or window fans to push air out of the space. If weather doesn't allow opening windows, use exhaust fans in bathrooms and kitchens, or run a portable air purifier with a HEPA and activated charcoal filter. Continuous air movement removes mould smell faster than any chemical treatment.

Keep fans and windows open for at least 48 to 72 hours after you've cleaned the mould. In humid climates or during humid seasons, keep ventilation running longer — mould smell lingers in moist air. If you have a basement or crawlspace with mould smell, run a dehumidifier to bring humidity below 50 percent, which slows mould growth and allows smell to dissipate.

Treat Walls and Hidden Spaces with Vinegar or Hydrogen Peroxide

If mould smell is coming from inside walls or under flooring but you can't see the mould, you can try treating the area from the surface. Drill small holes (about 1/4 inch) in the wall or floor near the source of the smell, spaced 12 inches apart. Spray white vinegar or 3 percent hydrogen peroxide into the holes using a spray bottle with a thin nozzle. The liquid will soak into the material and kill mould growing inside.

This method works only if the mould is near the surface and the material isn't too wet. If the area is soaked or if the smell doesn't improve after two applications, the mould is likely too deep or too extensive to treat this way, and the affected material will need to be removed. After spraying, leave the holes open or cover them loosely with tape to allow the material to dry.

Replace Heavily Affected Porous Materials

Drywall, carpet, insulation, and wood that are saturated with mould or mould smell often can't be fully cleaned. Once these materials are colonized by mould, the smell is embedded throughout, not just on the surface. Replacing them is faster and more reliable than trying to neutralize the odour.

If mould has been growing in a wall for weeks or months, the drywall behind it has absorbed moisture and mould smell deep into its layers. Cutting out the affected section and replacing it with new drywall stops the smell at the source. The same applies to carpet — if mould smell is coming from underneath, the carpet and padding need to be removed and the subfloor treated and dried before new flooring is installed.

Frequently Asked Questions

How long does it take for mould smell to go away?

If the mould is cleaned and you run fans and open windows continuously, the smell usually fades within three to seven days. If the smell lingers after a week, mould is still growing somewhere — check inside walls, under flooring, and around pipes. Smell that returns after you've cleaned indicates the mould wasn't fully removed.

Can I use bleach to get rid of mould smell?

Bleach kills surface mould but doesn't penetrate porous materials well and doesn't remove smell that's already absorbed into walls or carpet. White vinegar and hydrogen peroxide are more effective for both killing mould and neutralizing odour. Bleach also produces fumes that can irritate your lungs, especially in poorly ventilated spaces.

Will an air purifier remove mould smell?

An air purifier with both a HEPA filter and an activated charcoal filter will reduce mould smell in the air, but only while it's running. It won't remove smell that's trapped in materials like carpet or drywall. Use an air purifier alongside ventilation and absorbents like baking soda for faster results.

What if the smell is coming from the basement or crawlspace?

Basements and crawlspaces stay damp, so mould keeps growing and producing smell. Run a dehumidifier to keep humidity below 50 percent, open any basement windows, and run a fan to move air out. If the smell is strong, there's likely active mould growth on wood, insulation, or concrete — inspect the space for visible growth and treat it with vinegar or hydrogen peroxide.

Is mould smell dangerous to breathe?

Mould smell itself isn't toxic, but it indicates mould is present and releasing spores. Breathing mould spores can trigger allergies, asthma, and respiratory irritation in sensitive people. The smell is a signal to find and clean the mould, not just to mask the odour.