White Mold in the House: How to Identify It, What Causes It, and How to Remove It

White mold is not a single species. It is a description: many common molds look white or pale gray when they first grow, or stay that way on certain materials. It turns up most often where air is damp and still, such as basements, attics, crawl spaces, and closets. Because it blends into light-colored drywall and wood, people often notice the smell before they see the growth.

White mold is handled the same way as any other mold. The CDC's guidance is that it is not necessary to identify the type of mold, because all molds should be treated the same with respect to health risks and removal. What matters is how much there is, what it is growing on, and where the water is coming from.

What white mold looks like

• Texture: fuzzy, cottony, or powdery, sometimes in a thin film that looks like dust
• Color: white to pale gray, sometimes turning green, gray, or black as it ages
• Pattern: patches or spots that spread, often heaviest where moisture is highest
• Smell: musty or earthy, often stronger in a closed room

It is easy to mistake for dust. One quick check: dust wipes off cleanly and evenly, while mold tends to smear, leaves a stain, or grows back in the same spot.

White mold or efflorescence?

This is the most common question about white growth on basement walls. Efflorescence is not mold. It is a salt deposit left behind as water moves through concrete, block, or brick and evaporates.

Efflorescence is still a warning sign: it means water is moving through the wall. Where there is efflorescence, check nearby framing, drywall, and stored boxes for mold. See mold in the basement.

What causes white mold

Mold needs moisture, something to feed on, and time. White mold in a house usually traces back to one of these:

• Damp air. The EPA recommends keeping indoor humidity below 60 percent, ideally 30 to 50 percent. Basements and closed-up rooms often run higher.
• Leaks. Roof leaks, plumbing leaks, and condensation from ducts or pipes.
• Ground moisture. Water moving through foundation walls and slabs, especially in basements and crawl spaces.
• Poor ventilation. Attics with blocked vents, bathrooms without fans, and closets on exterior walls.
• Food. Wood, drywall paper, cardboard, fabric, and household dust are all organic and feed mold.

Where white mold grows

Basement

On wood framing, the bottom of drywall, stored cardboard boxes, and carpet. Usually from ground moisture, a leak, or summer condensation on cool walls.

Attic

On roof sheathing and rafters, usually from a roof leak, blocked soffit or ridge vents, or a bathroom fan that vents into the attic. See mold in the attic.

Crawl space

On floor joists, the subfloor, and insulation, from ground moisture and humid outdoor air. See mold in the crawl space.

Furniture, closets, and fabric

On leather, wood furniture, and clothing in closed closets, especially in a home that sits closed in humid weather.

White mold on wood: how bad is it?

Surface growth on solid wood is common and usually fixable. The real question is whether the wood itself is damaged. Push a screwdriver into the wood near the growth. If it is firm, the growth is likely on the surface; the wood can be cleaned, dried, and, on framing, lightly sanded while wearing a respirator. If the wood is soft, stringy, or crumbles, it may be decayed, which is a structural concern that should be evaluated and repaired.

Does turning the AC off cause mold?

In humid climates, it can. Air conditioning removes moisture from the air as it cools. A home left closed with the AC off in summer can rise well above the EPA's recommended limit of 60 percent humidity (ideally 30 to 50 percent), and white mold on furniture, cabinets, and closet walls is a common result. If you leave for weeks or months, keep the AC running at a moderate setting or use a dehumidifier, and keep interior doors open so air moves. This is a frequent issue for seasonal homes in places like Jacksonville and the rest of Florida.

How to remove white mold

For a small area, under about 10 square feet by the EPA's guideline, on a surface that is otherwise sound:

1. Fix the moisture. Otherwise it will return.
2. Protect yourself. N-95 respirator, gloves, and goggles; keep others out of the area.
3. Mist lightly to keep spores from becoming airborne.
4. Scrub hard surfaces and solid wood with detergent and water.
5. Remove porous materials with mold growth, such as drywall, insulation, carpet, and cardboard, and bag them before carrying them out.
6. Dry thoroughly with fans and a dehumidifier.
7. Check after a few weeks. Growth that returns means moisture is still getting in.

The EPA does not recommend bleach as a routine part of mold cleanup, and no spray makes it safe to leave moldy drywall or insulation in place. See how to remove black mold safely; the steps are the same for white mold.

Not sure how far it goes behind the drywall? A local inspector can check with a moisture meter, and the call to find one is free.

When to call a professional

• The growth covers more than about 10 square feet
• It is on insulation, drywall, or the subfloor
• It is in a crawl space or attic you cannot work in safely
• The wood is soft or crumbling
• It returns after cleaning
• Someone in the home has asthma, allergies, or a weakened immune system

What it costs

Removing mold from a small area typically runs about $500 to $1,500, according to HomeGuide's cost data. Basements, attics, and crawl spaces cost more because of access and the moisture work that goes with them. See our mold remediation cost guide.

White mold by region

Basements and crawl spaces are where most white mold shows up, which makes it a common call in Denver, Colorado Springs, and Fort Collins, where many homes have basements, and in older rowhouses in Washington, DC. In humid Florida, it is more often found on furniture, closets, and AC closets in homes that sat closed.

Next step

If you own your home and white mold covers more than a small area, is on drywall or insulation, or keeps coming back, call the number on this page to be connected with an independent local mold remediation company.