Mold and Indoor Air Quality Statistics (2026)

About 47% of US homes have dampness or mold conditions, based on a synthesis of national studies.

Roughly 3,800,000 occupied US homes reported signs of mold in the previous 12 months, per the American Housing Survey.

About 11,400,000 occupied US homes reported water leakage from outside the home, per the American Housing Survey.

About 10.4% of US homes had water damage from exterior leakage.

About 8% of US homes had water damage from interior leakage.

Dampness and mold problems occur in roughly 1 in 6 dwellings across Europe (about 16.5% show one or more indicators).

One third to one half of all buildings have damp conditions that can encourage mold and other biological growth.

The EPA recommends keeping indoor relative humidity below 60% to limit mold growth.

The EPA advises keeping indoor relative humidity ideally between 30% and 50%.

If wet or damp materials are dried within 24 to 48 hours after a leak or spill, in most cases mold will not grow.

In an EPA survey of representative US public and commercial office buildings, 85% had past water damage.

In that same EPA office-building survey, 45% had current water leaks at the time of assessment.

Americans spend roughly 90% of their time indoors, where exposure to indoor pollutants concentrates.

Indoor levels of common pollutants are often 2 to 5 times higher than typical outdoor levels.

An estimated 21% of current US asthma cases are attributable to dampness and mold exposure in homes.

Of the 21.8 million US asthma cases studied, about 4,600,000 were estimated to be attributable to dampness and mold in the home.

Homes with visible or documented mold issues often sell for 10% to 30% below market value, depending on severity and region.

Even after professional remediation, as many as half of prospective buyers walk away when they learn a property once had mold.

The national average cost of mold remediation is about $2,368, with most homeowners spending between $1,223 and $3,753.

Mold removal typically runs $10 to $25 per square foot of affected area.

Removing mold from a small, contained area commonly costs $500 to $1,500.

Extensive whole-house remediation can reach $10,000 to $30,000.

Confirmed black mold (Stachybotrys) usually costs 15% to 25% more to remediate due to added lab testing, PPE and clearance steps.

The EPA advises consulting its remediation guide (and often a professional) when mold growth covers more than 10 square feet.

EPA guidance recommends full containment for mold contamination greater than 100 square feet.

The annual US cost of asthma morbidity attributable to dampness and mold is estimated at $15.1 billion.

The annual US cost of allergic rhinitis attributable to dampness and mold is estimated at $3.7 billion.

The annual US cost of acute bronchitis attributable to dampness and mold is estimated at $1.9 billion.