Why Does My Washing Machine Smell After Sitting Overnight?

If your washing machine smells after sitting overnight, the odor is usually caused by trapped moisture, bacteria growth, or stagnant water in the drain system.

The smell may not be noticeable immediately after a cycle, but becomes stronger after the machine sits unused for several hours.

Here’s what causes it and how to fix it.

1) Residual Water in the Drum or Gasket

Small amounts of water often remain inside the washer after a cycle finishes.

When the machine sits closed overnight, that moisture creates the perfect environment for bacteria and mildew.

What to check:

• Wipe the inside of the drum
• Pull back the rubber door seal (front-loaders)
• Look for trapped water or buildup

Fix:

• Leave the washer door slightly open between loads
• Wipe moisture from the gasket after each use

2) Water Sitting in the Drain Hose

Water can remain in the drain hose after a cycle. If the hose design or placement traps water, it can create odor overnight.

What to check:

• Make sure the drain hose isn’t pushed too far into the wall drain
• Check for kinks or sagging

If water can’t drain freely, smells can return quickly.

3) Bacteria Inside the Washer Tub

Even if the washer looks clean, bacteria can grow in hidden areas.

This is especially common with:

• Cold wash cycles
• Excess detergent use
• High-efficiency machines

Fix:

• Run a hot cleaning cycle with white vinegar
• Follow with a second cycle using baking soda
• Use washer cleaner monthly

4) Sewer Gas From the Drain

If the smell is stronger near the wall drain, sewer gas may be backing up when the machine isn’t running.

This is less common, but possible.

If the odor smells strongly like sulfur or rotten eggs, it may be related to drain bacteria.

When It’s Not a Simple Cleaning Issue

Call a plumber if:

• The odor is strong throughout the laundry room
• Cleaning doesn’t improve the smell
• You suspect drain or venting problems

Most overnight washer odors are caused by moisture and bacteria buildup.

Quick Recap

If your washing machine smells after sitting overnight, check:

• Residual water in the drum
• Door gasket moisture
• Drain hose placement
• Bacteria buildup

Simple cleaning and airflow usually solve the problem.