Why There’s a Mildew Smell in Your House & What to Do
If your house has a mildew smell, there is a moisture issue somewhere that needs attention. This odor is more than just a nuisance. It can signal hidden damage, air quality concerns, and even health risks for your household.
Mildew thrives in dark, damp spaces, and the odor it produces tends to linger. It can start in small places, like under sinks or inside closets, and spread without you realizing it. The sooner you address the smell, the better chance you have of stopping a bigger problem before it starts.
What Causes That Musty Smell?
A mildew smell comes from microscopic fungal growth that starts when moisture combines with organic material in your house. Even if you cannot see any visible stains or mold patches, the smell alone suggests that spores are present. About 47% of U.S. homes show visible mold growth or water damage, often in damp, poorly ventilated rooms like bathrooms.
Some of the most common causes include:
- Leaky plumbing under sinks or behind walls
- Roof leaks or poor attic ventilation
- Clogged gutters or water pooling near the foundation
- HVAC units or ductwork with trapped moisture
- High indoor humidity with inadequate airflow
- Wet materials like carpet, insulation, or drywall that never fully dried after a spill or flood
These issues often develop slowly. You might first notice the smell after it rains, after running your HVAC system, or when returning to a closed-up room that has not been used in a while.
Health Risks from Mildew and Moisture
Most mildew odors do not pose an immediate health risk, but over time, exposure to mildew spores can cause symptoms in sensitive individuals. Common reactions include:
- Headaches
- Sneezing or coughing
- Eye or throat irritation
- Fatigue
- Asthma flare-ups
If the odor persists or gets stronger, it may point to growing mold colonies that can be more harmful. Homes with babies, elderly residents, or anyone with breathing conditions should be especially cautious.
Even beyond health concerns, mildew odors can impact the overall feel and function of your home. Guests may notice the smell right away, and if you plan to sell your house, a strong odor could turn buyers away or raise red flags during inspection.
How to Track Down the Source of the Smell
To get rid of the mildew smell, you first need to find out where the moisture is coming from. Start with the most common problem areas:
Bathrooms and kitchens: Check under sinks, around tubs, and near toilets. Even a small leak can soak into surrounding materials and create mildew over time.
Basements and crawlspaces: These areas are prone to moisture buildup, especially after heavy rain or during humid months. Look for puddles, wet insulation, or water stains on concrete walls or floors.
HVAC system: Condensation or clogged drain lines can cause mildew in ductwork. If the smell worsens when the air conditioning runs, your system may be involved.
Laundry rooms and closets: If these spaces are not properly ventilated, damp clothing or appliances can lead to mildew buildup.
Use your nose as a guide, but also inspect for visible signs of damage. Water stains, peeling paint, swollen baseboards, or warped flooring can all point to moisture intrusion. If you notice multiple areas with similar smells, the problem could be widespread.
What You Can Do Right Now
Here are some simple steps to try before calling in a professional:
- Open windows to improve airflow
- Run fans or dehumidifiers to reduce humidity
- Clean affected surfaces with white vinegar or a mildew-specific cleaner
- Remove damp items like rugs, boxes, or clothing that may be holding moisture
- Seal up obvious gaps or cracks where water could be entering
- Replace air filters and schedule HVAC maintenance if needed
If these steps help, but the smell returns a few days later, that is a sign the root issue has not been fully resolved.
When to Get a Home Inspection
If you cannot locate the source of the smell, or you suspect it may be coming from inside walls, the attic, or your HVAC system, it is time to call in a licensed home inspector.
Inside & Out Property Inspectors can:
- Check behind walls and under floors using thermal imaging
- Examine the roof, attic, foundation, and crawlspaces for signs of water damage
- Evaluate ventilation and airflow to identify where humidity is building up
- Recommend whether mold testing or remediation is needed
Because mildew can come from so many sources, an experienced inspector brings the tools and knowledge to find what you cannot see.
Common Questions About Mildew and Moisture
Can a mildew smell really affect the value of my house?
Yes. A strong odor can lead to lower offers or failed sales. Buyers assume odors mean hidden problems, and many won’t risk it unless the issue is clearly fixed.
Do I need mold testing too?
Not always. A home inspection comes first. If there are visible signs of mold or if the odor is strong and persistent, your inspector may recommend air quality testing or a mold specialist.
Could this be a roof problem?
It could. Roof leaks are one of the leading causes of mildew in attics, ceilings, and walls. Even a small leak can trap moisture for weeks before you notice it.
What if I already had the home inspected before buying?
Things can change fast. A previously dry crawlspace can flood during a storm. New leaks can appear after roof damage. Mildew odors should never be ignored, even in newer homes.
Can this tie into foundation issues?
Yes. If your foundation is not draining properly or if water collects near the base of the home, moisture can wick into walls and floors, leading to mildew or mold growth.
Why This Matters for Jacksonville Homes
In our climate, homes are always at risk for moisture-related issues. That makes mildew smell a more common problem here than in many other states. At Inside & Out Property Inspectors, we see these conditions often and know where to look first.
If you live in the Jacksonville area and notice a musty odor that won’t go away, don’t wait for bigger problems to show up. Schedule a home inspection to get clear answers and recommendations you can trust.
Final Thoughts
A mildew smell in your house is an issue of safety, air quality, and long-term maintenance. You may be able to clean the surface or mask the odor temporarily, but until the root issue is addressed, it will keep coming back.
A home inspection gives you the clarity to move forward confidently, whether that means a quick repair, better ventilation, or more advanced remediation. Get your inspection scheduled with Inside & Out today.