Category
Mold Basics & Health
What mold is, why it grows indoors, and what the science says about its effect on health.
Topics
- What mold is and why it grows indoors Mold is a fungus. Its spores are in every breath of outdoor and indoor air, and that is normal. A spore only becomes a problem when it lands somewhere wet and has... Best practice
- How mold affects health The most common effects are allergic: sneezing, runny nose, red eyes, rash. Mold can trigger asthma attacks in people who are sensitized to it, and it irritates the... Best practice
- Mycotoxins, “toxic black mold” and musty odors Some molds can produce toxins (mycotoxins) under certain conditions — more than 200 have been identified. But finding mold in a building doesn't mean toxins are... Best practice
- What grows after water damage — and why speed matters Bacteria and fungi live in ordinary household dust and on building materials, and in a dry, routinely cleaned home they cause no trouble. Once water gets in or... Best practice
- Health risks from water damage and sewage The S500 treats microbial contamination after water damage as a public health problem for both occupants and workers. Floodwater brings soil bacteria and fungi that... Best practice
- How mold grows indoors: spores, hyphae and shifting ecology Molds are microscopic fungi that feed on dead organic material. They spread as spores too small to see. When a spore lands somewhere with enough moisture and a... Best practice
- What health agencies conclude about damp buildings Chapter 3 reviews what national and international bodies had concluded about damp, moldy buildings and health. R520 reports that the Institute of Medicine found... Best practice
- Allergy, toxins and infection: how mold may affect health R520 describes three ways mold exposure may affect people. Allergy affects only people who are already sensitized, and it explains runny nose, watery eyes and asthma... Best practice
- Occupant health, relocation and remediation worker risk When people in a building report symptoms, R520 recommends a physician experienced with indoor air problems, ideally brought in before or alongside the building... Best practice
Questions & answers
What causes mold to grow in my home?
Mold grows when moisture meets a surface it can feed on — drywall, wood, carpet, ceiling tiles. Mold spores are always present in the air; they only become a problem when they land on something wet. The key fact every Texas homeowner should know: if something stays wet for more than 24–48 hours, mold will almost certainly start growing. In humid Texas summers, that timeline can be even shorter. Fix the water source first — without that, cleaning mold is temporary.
Based on: EPA Brief Guide to Mold Moisture and Home (EPA 402-K-02-003)
Can mold grow without visible water damage?
Yes. Mold doesn't need standing water. High indoor humidity above 60%, condensation on pipes or windows, or slow hidden leaks inside walls are all enough. In hot, humid climates such as Texas, air conditioning can create condensation in attics and wall cavities when warm humid air meets cold surfaces. If you smell something musty but can't see any mold, hidden growth is the likely culprit — behind drywall, under flooring, or inside HVAC ductwork.
Based on: EPA Brief Guide to Mold Moisture and Home (EPA 402-K-02-003)
Is it possible to eliminate all mold from my home?
No — and anyone who promises 100% mold elimination is being misleading. Mold spores exist naturally in outdoor and indoor air everywhere on earth. The goal of mold remediation is not to reach zero spores but to return indoor mold levels to normal background levels and eliminate any active growth. A successful remediation means no visible mold, no musty odor, no moisture problem, and no health complaints from occupants. In Texas, that means also resolving whatever moisture source allowed growth in the first place.
Based on: EPA Brief Guide to Mold Moisture and Home (EPA 402-K-02-003)
What health problems can mold exposure cause?
Mold exposure can trigger a range of health effects depending on the person and the level of exposure. Common symptoms include sneezing, runny nose, red and watery eyes, skin rash, and coughing — essentially allergy-like reactions. For people with asthma, mold can trigger attacks. Those with weakened immune systems face more serious risks, including fungal lung infections. Children are especially vulnerable — research published by NIH links household mold to childhood asthma. If symptoms consistently worsen at home and improve elsewhere, mold exposure is a serious possibility worth investigating.
Based on: AAFA Mold Allergy Symptoms Prevention Treatment; EPA Brief Guide
What are the symptoms of a mold allergy?
A mold allergy typically looks like persistent hay fever: runny nose with clear discharge, nasal congestion, postnasal drip, sneezing, and itchy or watery eyes. Some people also develop skin rashes. What distinguishes mold allergy from a cold is that symptoms persist and often worsen in damp or musty environments — basements, bathrooms, or after rain. Mold allergy can trigger immediate reactions or delayed ones. In rare cases, people develop allergic bronchopulmonary aspergillosis — a serious lung condition involving both allergic and inflammatory responses. If that describes your situation, see a pulmonologist or allergist.
Based on: AAFA Mold Allergy Symptoms Prevention Treatment
Who is most at risk from mold exposure?
The people at greatest risk from mold exposure are: (1) those with asthma or existing respiratory conditions, (2) people with allergies — especially mold allergies, (3) infants and young children, (4) the elderly, and (5) anyone with a weakened immune system, including those on immunosuppressive medications or undergoing chemotherapy. In Texas, flood events from hurricanes and severe storms mean many homeowners encounter mold after water intrusion — and these vulnerable groups should not participate in any mold cleanup work at all. If anyone in your household fits these categories, call a professional.
Based on: CDC Homeowner's Guide to Mold Cleanup After Disasters; AAFA
What is black mold and how dangerous is it?
Black mold usually refers to Stachybotrys chartarum — a greenish-black mold that grows on wet, cellulose-rich materials like drywall paper, wood, and ceiling tiles after prolonged moisture exposure. Stachybotrys is a tertiary colonizer, requiring continuously wet conditions to grow. Finding it signals a serious, sustained moisture problem. The IICRC S520 Standard notes that Stachybotrys is capable of producing mycotoxins — toxic compounds that can be present on spores and fungal fragments. The CDC has stated that urgency of remediation should not necessarily be greater simply because a mycotoxin-producing fungus is identified. That said, confirmed presence warrants urgent risk management decisions. Not all black mold is Stachybotrys, and Stachybotrys is not the only mold of concern. Only laboratory analysis can identify mold species.
Based on: IICRC S520 Standard for Professional Mold Remediation (3rd Ed.)
How does mold affect office buildings and commercial spaces differently than homes?
Commercial and office buildings present unique mold challenges. The scale is larger — a single HVAC system may serve thousands of square feet. Buildings with flat roofs, complex plumbing, and large glass facades are particularly vulnerable to water intrusion and condensation. Because commercial HVAC systems recirculate air across large zones, a single mold source can affect occupants far from the contamination point. Building materials in commercial construction — particularly fiberglass duct liner and ceiling tiles — are highly susceptible to mold when moisture is present. Unlike a homeowner who lives with the problem and notices it quickly, building managers may not be aware of mold developing in ceiling plenums, mechanical rooms, or behind walls until occupants start complaining.
Based on: OSHA; CCOHS
Is black mold always Stachybotrys chartarum?
No — and this is one of the most important myths to debunk. Black mold is a color description, not a species. Many mold species can appear black or dark green: Aspergillus niger, Cladosporium, Ulocladium, Nigrospora, and others. Stachybotrys chartarum — the species most often associated with toxic black mold — is actually less common than the other dark-colored molds. Color alone cannot identify mold species. The only way to identify mold species is laboratory analysis — either from a surface sample or an air sample analyzed by a qualified mycologist. What matters most is the size of the problem, the moisture source driving it, and whether occupants are experiencing health effects.
Based on: EPA 402-K-01-001
Is black mold automatically more dangerous than other molds?
Not necessarily — and the fear around black mold has been significantly amplified beyond what the science supports. Research including reviews by the CDC and Institute of Medicine found that the evidence for unique toxicity was much weaker than media coverage suggested. Stachybotrys can produce mycotoxins under certain growth conditions, but it grows slowly, produces relatively few airborne spores compared to other molds, and is not always in a toxin-producing state. Other mold species — Aspergillus, Penicillium, Chaetomium — can also produce mycotoxins and may be present in much higher airborne concentrations. All mold growth in a home is a problem worth addressing: molds can trigger allergic reactions, asthma attacks, and respiratory irritation regardless of species.
Based on: EPA 402-K-01-001