Humidity refers to the amount of moisture present in the air. Indoors, it’s measured as relative humidity (RH) — a percentage that tells you how much moisture the air is holding relative to its maximum capacity.
The EPA recommends keeping indoor humidity below 60%, with an ideal range of 30% to 50% relative humidity. A basic humidity monitor — available at most hardware stores for as little as $10 to $50 — is all you need to know where your home stands.
In South Florida, staying within that range is a genuine challenge. Outdoor humidity regularly exceeds 80% during summer months, and that moisture is constantly trying to find its way inside.
Most humidity guidance is written for climates that have a dry season. South Florida doesn’t really have one. The consequences of that are significant:
Mold growth — Mold begins to grow when indoor humidity stays above 60% for extended periods. In South Florida that threshold is easy to cross, especially in closets, bathrooms, behind walls, and inside AC systems.
Dust mites — Dust mites thrive in humid environments. They’re one of the most common indoor allergens and a leading trigger for asthma, particularly in children.
Structural damage — Prolonged excess moisture warps wood, peels paint, damages drywall, and can compromise the structural integrity of a building over time.
Poor AC performance — When humidity is high, your AC system works harder to cool your space because it’s removing moisture as well as heat. An oversized or poorly maintained system may cool the air too quickly without removing enough moisture, leaving you cold but still humid.
Comfort — High humidity makes air feel warmer than it is, meaning many South Florida residents are overcooling their homes in an attempt to feel comfortable when the real problem is moisture.
Here’s a simple reference for South Florida residents:
Below 30% = Too dry. Uncommon in South Florida but possible in heavily air-conditioned spaces. Can cause dry skin, irritated airways, and static electricity.
40% – 50% = Ideal. The EPA and Consumer Product Safety Commission both recommend this range. Comfortable, healthy, and mold-resistant.
50% – 60% = Acceptable but worth monitoring. Mold risk increases as you approach 60%.
Above 60% = Problematic. Mold growth becomes likely. Dust mites thrive. Your AC system is struggling.
Above 70% = High risk. Mold can begin growing within 24 to 48 hours on wet surfaces at this level.
Humidity doesn’t only come from outside. Common indoor moisture sources include:
Browse our humidity and moisture topics below
When to use a dehumidifier, what size is needed, attic dehumidification, whole-home vs. portable units, and more.
learn more
What dew point actually means, why indoor humidity stays high, how temperature affects moisture levels, and more.
AC removes some moisture — but it’s not a dehumidifier. Learn why South Florida homes can feel humid even with the AC running, and what to do about it.
Water doesn’t have to be visible to be a problem. Learn how moisture enters South Florida homes.
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.