When I moved into my apartment, the bedroom closet smelled like a wet towel that had been forgotten for a week. I hung air fresheners everywhere, and the smell came right back.

The air fresheners were masking the real problem. A musty smell is almost always moisture hiding somewhere, and until you find it, the smell keeps coming back.

Check the bathroom first

The most common hidden source is the bathroom. A weak or broken exhaust fan leaves moisture in the air after every shower. Run the fan for twenty minutes after showering, and clean the fan cover if it is dusty. A working bathroom fan fixes more musty closets than anything else.

Look under the sinks

A slow drip under the bathroom or kitchen sink keeps the cabinet damp all day. Feel the pipes and the cabinet floor. Even a small leak creates a musty smell that spreads.

Check the washing machine

Front load washers collect water in the rubber gasket. Wipe the gasket dry after each load and leave the door open. A damp machine is a mold factory, and the smell travels through the whole laundry room.

Use a dehumidifier in the basement

Basements are damp by nature. A dehumidifier set to around 50 percent humidity makes a huge difference. Empty the tank regularly or hook it to a drain, and keep the humidity in check.

Air out the house

Even in winter, open windows for five minutes on a dry day. Stale, humid air needs to leave. If the outside air is drier than the inside air, a short airing helps.

Know when to call someone

If the smell comes with visible mold on walls or ceilings, or you find water stains, that is beyond a weekend fix. Call a mold inspector or plumber before it spreads.

My closet smells like laundry detergent now, and it took exactly one working bathroom fan to get there. The air fresheners went in the trash.