Gateway/Indoor mold
Indoor mold
Why mold grows inside homes, the moisture levels that prevent it, what testing can and cannot tell you, and when cleanup needs a professional.
| Cause | Moisture: leaks, flooding, condensation, high humidity |
|---|---|
| Prevention | Dry wet materials within 24 to 48 hours; keep indoor humidity below 60% |
| Federal limits | None set by EPA for indoor mold or spores |
| Standard | ANSI/IICRC S520 for professional remediation |
What it is
Indoor mold is fungal growth on materials inside a building. Mold spores are present in nearly all indoor and outdoor air, so the question is never whether spores are present but whether something indoors is wet long enough for them to grow. Once they do, mold digests the material it is on and releases more spores and odors.
What causes it
The U.S. Environmental Protection Agency (EPA) says the key to mold control is moisture control. Common sources in St. Louis homes are basement seepage and flooding, slow plumbing and appliance leaks, roof and window leaks after storms, condensation on cold surfaces, and humid summer air in basements and crawl spaces. The EPA advises drying water-damaged materials within 24 to 48 hours to prevent growth and keeping indoor relative humidity below 60 percent, ideally between 30 and 50 percent.
Health effects
The CDC says mold can cause a stuffy nose, sore throat, coughing or wheezing, burning eyes or a skin rash in some people. People with asthma or mold allergies may have severe reactions, and people with weakened immune systems or chronic lung disease can develop lung infections. Anyone with symptoms should talk to a doctor.
Testing and its limits
The EPA has not set federal standards or limits for airborne mold or spores, so sampling cannot show whether a home “passes” a legal threshold. Air and surface samples are useful for comparing indoor and outdoor spore types, locating hidden growth, documenting conditions for a sale or claim, and confirming that a remediated area is clean. See air sample, surface sample and clearance testing.
Cleanup
The EPA suggests a homeowner can often handle small areas (under about 10 square feet) if the moisture problem is fixed. Larger areas, growth inside walls or HVAC systems, growth after sewage or contaminated water, and homes with occupants who have health concerns call for professional remediation under the IICRC S520 standard, with containment, removal of affected porous materials, HEPA cleaning and verification. See mold remediation vs. removal.
Key takeaways
- Mold growth is a moisture problem; fix the water first.
- Dry wet materials within 24 to 48 hours and keep humidity below 60%.
- There are no federal mold limits, so testing documents conditions rather than proving compliance.
Related glossary terms
- Mold conditions 1, 2 and 3
- Air sample (spore trap)
- Surface sample
- Clearance testing (post-remediation verification)
- Mold remediation vs. mold removal
- Containment
- IICRC S520
Related services and guides
Identifiers
References
- EPA: A brief guide to mold, moisture and your home
- EPA: Mold testing or sampling
- CDC: About mold and your health
- Wikipedia: Indoor mold
Reviewed by Jake Lusby, owner of Gateway Water & Mold. Part of our entity reference pages. See our editorial policy to report an error.
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