Mold is a type of fungus found naturally in both indoor and outdoor environments. Tiny particles called spores travel through the air constantly — and when they land on a wet or damp surface indoors, they can begin to grow and spread.
According to the U.S. Environmental Protection Agency, mold is not typically a problem unless it begins growing indoors. The key to controlling it is controlling moisture.
In South Florida, that’s easier said than done. With average humidity levels regularly exceeding 70%, mold doesn’t just show up after a flood or a leak — it can grow behind walls, under floors, inside AC ducts, and in any space where moisture lingers.
Year-round humidity above 60% — the threshold at which mold growth accelerates
AC systems running constantly, which can harbor mold in ducts, drain pans, and coils if not properly maintained
Hurricane and storm season bringing moisture intrusion, flooding, and hidden water damage
Concrete and stucco construction that can trap moisture inside walls
Condos with shared HVAC systems, where one unit’s moisture problem can affect neighbors and responsibility for remediation is often unclear
The Florida Department of Health notes that virtually every building in Florida will support mold growth at some point. The question is not if — it’s when, and how much.
According to the EPA, mildew is actually a type of mold — not a separate category. The term is generally used to describe mold with a flat growth habit. Mildew often lives on shower walls, windowsills, and other places where moisture levels are high.
Mold, more broadly, refers to microscopic fungi that can thrive on almost any organic material — walls, ceilings, wood, paper, clothing, and leather. In unaired spaces like closets or bathrooms, both can produce a strong musty odor.
The bottom line: whether you call it mold or mildew, the cause is the same — moisture.
Browse our mold & mildew topics below
Mold is a fungus — and there are thousands of species. Learn about the most common types found indoors.
learn more
Can mold make you sick? What are the real symptoms of mold exposure? We break down the science on allergies, respiratory effects, and the truth behind “mold poisoning” — without the myths.
Not sure if you have mold? Learn the signs, explore DIY test kits, and understand when a professional inspection is necessary.
Can you paint over mold? Can you clean it yourself? We cover what mold removal actually entails, when DIY is appropriate, and when you need a licensed Florida remediation professional.
We’re here to help. Whether you’re trying to learn about pollutants in your home or workplace, or just want to point us toward a topic you’d like us to cover — we’d love to hear from you.
South Florida Indoor Air is an independent educational resource dedicated to helping our community breathe better and make informed decisions about the air inside their spaces.