You might expect a musty smell from a basement or a damp garage, but you probably don't expect to encounter it coming out of your drainpipes. If you notice a musty odor in your home's drains, its a warning that they need cleaning to bring a fungus problem under control.
A musty smell can occur in any drainpipe of your home, from the one in your shower to the one behind your washing machine. The foul, earthy smell wafts up through the drain and into your home. The odor will always be strongest right beside the drain. If you run water into it by washing your hands or taking a shower, the smell will fade for a few hours but soon returns. It is often worse in warm humid weather than in the winter.
The musty smell is caused by mold or mildew growing inside the drainpipe. Fungus thrives in dank, poorly ventilated areas like a drain. In addition, each drainpipe contains a small reservoir of water in a curving section known as a trap. Mold and mildew feed on organic debris built up inside the pipe and the water in the trap. Exposure to the musty odor isn't just unpleasant; if you are sensitive to their spores, mold and mildew can trigger health problems like eye and skin irritation, along with respiratory issues.
Getting rid of the fungus will clear out the earthy smell. Drain cleaner won't solve the problem. Instead, pour 1/2 c baking powder into the stinky drain. Wait about 20 minutes, then pour in 1 c hydrogen peroxide, which will foam up, coating the inside of the drainpipe. Hydrogen peroxide is an oxidizer and will kill the fungus, while baking powder works as a deodorant to get rid of the smell. Let them sit for a couple hours, then wash them down the drain by running hot water into it.
If mold returns to a drainpipe, it will bring back the musty smell. If you have drains that have been problems in the past, make preventing the return of fungus a part of your monthly cleaning routine. Pour 1 c vinegar into each problem drain every month. Vinegar is strong enough to kill mold and mildew spores before they get established, and it helps deodorize your pipes before the smell gets bad. You can rinse the vinegar out after an hour, or let it sit until the next time you use the drain.