Homeowner guide
Signs of Mold in Your Home (and What a Musty Smell Means)
Mold doesn’t always show itself. Often the first clue is a smell, a stain or allergy symptoms that only happen at home. Here’s how to read the signs, where to look, and when it’s time for a professional.
- A musty, earthy smell is the most common sign of hidden mold.
- Other signs: stains, peeling paint, warped baseboards, condensation and symptoms that ease when you leave.
- In Florida homes, check the AC closet, bathrooms, under sinks, windows and the attic first.
- If you smell mold but can’t find it, a professional inspection with moisture mapping is the next step.
9 warning signs of mold
- A musty smell that’s stronger in one room, a closet or when the AC turns on
- Visible spots: black, green, gray or white, fuzzy or slimy
- Water stains on ceilings or walls
- Bubbling, peeling or cracking paint
- Warped or soft drywall, baseboards or flooring
- Condensation on windows, AC vents or cold water pipes
- Indoor humidity over 60%
- A past leak or flood, even if it looked dry afterward
- Allergy-like symptoms (stuffy nose, sneezing, itchy eyes) that ease when you leave home
What a musty smell means
Growing mold gives off gases called microbial volatile organic compounds (MVOCs). They cause the earthy, damp-basement smell most people recognize. A musty smell usually means mold is actively growing somewhere nearby, even if you can’t see it.
| Where the smell is strongest | Likely source |
|---|---|
| When the AC turns on | Air handler, coil, drain pan or ducts |
| Bathroom or closet | Shower walls, behind vanity, poor ventilation |
| Under the kitchen sink | Slow drain or supply line leak |
| Whole house after being closed up | High humidity throughout |
| Near a window or slider | Rain getting in around the frame |
| Upstairs ceiling or garage | Attic leak or ventilation issue |
Where mold hides in Florida homes
- Air handler closets and supply vents
- Under and behind sinks, toilets, dishwashers and washing machines
- Shower and tub walls, especially behind tile
- Window frames, sills and sliding door tracks
- Closets on exterior walls
- Attic decking and insulation
- Behind furniture pushed against exterior walls
What you can check yourself
- Follow your nose. Note where the smell is strongest and when.
- Check humidity with an inexpensive hygrometer. Aim for 30% to 50%.
- Look under sinks with a flashlight for drips, stains or swollen cabinet floors.
- Check the AC closet and drain pan for standing water.
- Look at ceilings under bathrooms and in rooms below the attic.
- Press on drywall near showers and windows. Soft spots mean moisture.
Don’t open walls, scrape or sand suspected mold yourself. Disturbing it can release spores into the air.
When to call a professional
- You smell mold but can’t find it
- The area is larger than about 10 square feet
- Mold is in the AC, walls or attic
- The home took on flood or sewage water
- Someone in the home has asthma, allergies or a weakened immune system
- You need documentation for insurance, a landlord or a sale
Frequently asked questions
Can you smell mold if you can’t see it?
Yes. A musty smell is often the first sign of mold growing inside walls, under floors or in the AC system.
Does a musty smell always mean mold?
Not always, but it usually means moisture. Damp carpet, a dirty drain or a wet towel can smell musty too. If the smell lingers, look for mold.
What does mold smell like?
Most people describe it as earthy, damp, stale or like an old basement or wet socks.
Can mold make my house smell even if it’s clean?
Yes. Mold can grow on the back of drywall, inside the AC or in the attic, out of sight of normal cleaning.
How do I get rid of a musty smell for good?
Find and remove the source and fix the moisture problem. Air fresheners and sprays only cover the smell.
Smell mold but can’t find it?
A moisture survey and testing will find the source.