How to get rid of mold on walls: what EPA and CDC guidance says
By Dan Whitlock, Home Projects Editor · Updated October 2026
The EPA says a moldy area under about 10 square feet (roughly 3 ft by 3 ft) is, in most cases, something you can clean yourself: fix the moisture source, scrub hard surfaces with detergent and water, and dry them completely. Larger areas, mold inside the wall, or damage from sewage or flooding call for professional help.
What people usually report
Spots or patches in black, green, gray, or white on painted drywall, often in a corner, behind furniture on an outside wall, or near a bathroom or window. Wiping removes the surface color, and it comes back weeks later.
What official sources say this can mean
These are possible causes listed in published guidance. They are not a diagnosis of your home; only an inspection can tell which, if any, applies.
- Condensation in cold corners and on outside walls behind furniture, where air does not circulate. (EPA)
- A plumbing or roof leak inside the wall cavity wetting the back side of the drywall. (EPA; EPA)
- High indoor humidity from cooking, showers, or unvented appliances. (EPA)
- Mold that was painted over. The EPA says paint applied over moldy surfaces is likely to peel. (EPA)
Who should not clean mold, and when to stop
- The CDC says people with mold allergies, asthma, COPD, other lung disease, or a weakened immune system should not take part in cleanup.
- The EPA says to bring in a professional with experience in contaminated-water damage if the water or mold came from sewage, and to follow its professional remediation guidance for areas over about 10 square feet.
- Never mix bleach with ammonia or other cleaners; the CDC warns this produces a poisonous gas.
How to find out
Check it yourself
- Measure the patch. Under about 10 square feet on a hard, painted surface is the size the EPA describes as a homeowner job in most cases. (EPA)
- Find and stop the moisture first. A moisture meter on the wall around the patch shows whether the drywall is wet from behind. (EPA)
- Gear up the way the CDC describes: at least an N95 respirator, non-latex gloves, and goggles without open vent holes. (CDC)
- Scrub with detergent and water and dry completely. The EPA says chemical biocides such as bleach are not recommended as a routine practice; the CDC says if you use bleach, no more than 1 cup per gallon of water. (EPA; CDC)
- Replace drywall that stays moldy or soft. The EPA notes porous materials may have to be thrown away because mold can be impossible to remove from them completely. (EPA)
When to call a licensed professional
- For more than about 10 square feet, mold inside the wall, or sewage-related damage, the EPA directs homeowners to professional remediation; ask contractors to follow EPA or ACGIH remediation guidelines.
- Some states license mold assessors and remediators. Texas, Florida, and New York run public license lookups.
Try this while you wait
Screening tools that help you gather facts before a professional visit. They do not diagnose anything and are no substitute for a licensed pro. As an Amazon Associate we may earn from qualifying purchases, and it never changes your price. Affiliate disclosure.
- Moisture meters on Amazon →
Shows whether drywall, wood trim, or framing is still wet, so you can tell an old stain from an active leak.
- NIOSH-approved N95 respirators on Amazon →
The CDC says to wear at least an N95 when cleaning mold.
- Non-vented goggles on Amazon →
The CDC notes that safety glasses or goggles with open vent holes will not keep out dust and small particles.
- Digital humidity monitors (hygrometers) on Amazon →
Reads indoor relative humidity. EPA guidance is below 60 percent, ideally 30 to 50 percent; CDC says no higher than 50 percent.
- Dehumidifiers on Amazon →
CDC and EPA both list a dehumidifier as a way to keep humidity down while you track the source.
Local help
We do not recommend or vet specific businesses. The official lookups above are the neutral way to check a license. The block below is advertising from our partner Angi.
Get quotes from local pros
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Angi pays us a referral fee for a completed service request. The fee comes from Angi, not from you, and it does not change the estimates on this page.
What the fixes cost
Frequently asked questions
What kills mold permanently on walls?
Nothing keeps mold away permanently while the wall stays damp. The EPA says the key to mold control is moisture control, and that mold will most likely come back if you clean it without fixing the water problem. Cleaning removes the growth; drying the wall and fixing the leak or humidity is what stops the return.
Will bleach kill mold on walls?
The EPA says using a biocide such as chlorine bleach is not recommended as a routine part of mold cleanup, and that dead mold can still cause allergic reactions, so it has to be removed, not just killed. The CDC says bleach can be used on hard surfaces at no more than 1 cup per gallon of water, never mixed with ammonia or other cleaners.
Can you kill mold without removing drywall?
On the painted surface of sound drywall, usually yes: scrub, dry, and watch for regrowth. The EPA notes that porous materials can hold mold in their crevices, so drywall that is soft, stained through, or moldy on the back side may need to be cut out and replaced.
How harmful is mold on walls?
The CDC says exposure to damp and moldy environments may cause a range of effects, or none at all; mold can cause a stuffy nose, coughing, wheezing, or itchy eyes in sensitive people, and more severe reactions in people with asthma or mold allergies. Anyone with symptoms should talk with a health professional.
Related warning signs
Or see every guide in The Dry Home.
Sources
Official and technical guidance cited on this page, checked October 2026:
- EPA: Mold Course, Chapter 2 (moisture and mold investigation)
- EPA: A Brief Guide to Mold, Moisture and Your Home
- CDC: Mold Clean Up Guidelines and Recommendations
- CDC: Mold
- Texas TDLR: Mold Assessors and Remediators
- Florida DBPR: Mold-Related Services licensing
- New York State Department of Labor: Mold Program
This guide summarizes published guidance from EPA, CDC, Texas TDLR, Florida DBPR, NY DOL. Guidance can change and may not cover your situation; verify with the official source before making decisions. Not affiliated with any of these agencies or organizations. This page is general information, not medical, legal, insurance, or engineering advice, and it cannot diagnose a problem in your home.
Spot an error? Email a correction. Product links are Amazon affiliate links and the Angi block is a paid partnership; see our disclosure.