Why does my house smell musty?

A musty smell in your house almost always comes down to one thing: moisture hanging around where it shouldn’t. Even if you can’t see mold, damp air trapped inside walls, carpets, or ducts creates the perfect environment for bacteria and mildew that produce that stale, earthy odor.

The four most common culprits are high indoor humidity (anything above 60% encourages microbial growth), poor ventilation in bathrooms and basements, an HVAC system circulating dust and damp air through dirty filters or ducts, and hidden water damage from a slow pipe leak or roof drip you haven’t spotted yet.

Start with the easy fixes: run a dehumidifier to bring humidity below 50%, make sure bathroom and kitchen exhaust fans actually vent outside, and change your HVAC filter if it’s been more than three months. If the smell persists, check under sinks, around windows, and in attic corners for signs of water staining—the source may be behind a wall, not in plain sight.