Why Your Dishwasher Smells Bad (and How to Fix It)

A clean dishwasher should smell like… nothing. When it hits you with sour, musty, or rotten-egg odors, something inside the machine—or just upstream in your plumbing—needs attention. The good news: most smell problems come down to food debris, biofilm, or stale water and can be solved with a thorough clean and a few habit tweaks.

Before we dig in, a quick note: Appliance Rescue offers expert guides, tips, and troubleshooting advice only; they do not provide repair services or send technicians. If you have questions about this guide or want to share feedback, you can Contact us.

Quick diagnosis checklist (start here)

• Open the door and sniff: Is it sour, musty, fishy, or sulfur (“rotten egg”)? Odor type hints at the cause (see next section).
• Check the filter and sump: Pull the lower rack, twist out the filter, and peek into the sump. Visible gunk = likely culprit.
• Inspect the door gasket: Run a finger along the folds. Slime means trapped moisture + residue.
• Look under the bottom spray arm: Food chunks hide here; they rot and stink.
• Verify the drain path: If the dishwasher drains through a garbage disposal, run the disposal with water for 30 seconds first.
• Confirm a high loop or air gap: Without one, dirty sink water can backflow into the tub.
• Sniff the water line area: Burnt or plastic odors can indicate a wiring, heater, or melting plastic issue—uncommon but important.

What the smell is telling you

Sour or vinegary

Likely cause: Fermenting food residue on the filter, at the sump, or behind the lower spray arm.
Fix: Deep-clean the filter and sump, then run a hot sanitize cycle with a cleaning agent.

Musty, damp, or “gym bag”

Likely cause: Biofilm (a slimy bacterial layer) on the tub walls, gasket folds, and racks.
Fix: Remove racks, scrub gasket folds, and run a tub-clean cycle with a dishwasher cleaner or diluted bleach (see safety notes).

Rotten egg (sulfur)

Likely cause: Drain water backing up from the sink/disposal, or stagnant water trapped in the drain hose. Occasionally a water heater with sulfate-reducing bacteria.
Fix: Clear the disposal, verify a high loop/air gap, and flush the drain hose. If the smell appears at other fixtures too, sanitize the water heater (consult the manufacturer).

Fishy

Likely cause: Protein residues (fish, eggs, dairy) baked onto hidden surfaces.
Fix: Manual scrub of the spray arms, filter, and door edges; then a high-temp cycle with enzyme cleaner.

Hot plastic or burning

Likely cause: A plastic utensil slipped onto the heating element, or a rare electrical/element fault.
Fix: Remove melted plastic (when cool) and run a short cycle to confirm the smell is gone. If the odor persists or you see scorching, stop using the machine and consult a professional.

The definitive deep-clean (do this once, thoroughly)

Budget ~45–60 minutes. You’ll need a microfiber cloth, soft brush or old toothbrush, mild dish soap, white vinegar, baking soda, and—optionally—an enzyme dishwasher cleaner.

1. Power & prep: Turn off the dishwasher at the wall switch/breaker if accessible. Remove the bottom rack.
2. Filter removal: Unlock and lift out the filter mesh and the coarse screen. Soak them in warm, soapy water for 10 minutes; scrub gently and rinse well.
3. Sump inspection: With a flashlight, check the sump and inlet. Use a spoon or gloved hand to lift out debris (pasta, seeds, glass).
4. Spray arms: Pop off the lower (and upper, if easy) spray arms. Rinse. Use a toothpick to clear each jet hole.
5. Gasket & folds: Wipe the door gasket and the lower door lip. These folds harbor slime. A 1:4 vinegar-water mix cuts biofilm nicely.
6. Racks & tines: Wipe rack edges and utensil basket. Look for a peeling rack coating that can trap grime.
7. Tub rinse: Wipe the tub walls with warm, soapy water, then with clean water to remove suds.
8. Vinegar wash: Reassemble parts. Place a dishwasher-safe cup with 1–2 cups of white vinegar on the top rack. Run the hottest cycle.
9. Baking soda polish (optional): After the vinegar cycle, sprinkle ½ cup baking soda across the tub bottom and run a short hot cycle.
10. Enzyme cleaner (optional alternative): Use an enzyme-based dishwasher cleaner per label if you prefer a one-step approach.

Safety notes:

• Do not mix bleach with vinegar or ammonia. If using diluted bleach (non-stainless tubs only; check your manual), ventilate well and rinse thoroughly afterward.
• Use only cleaners labeled safe for dishwashers.

Parts worth a closer look

• Filter assembly: If the mesh is torn or warped, replace it; it won’t trap food properly.
• Door gasket: Cracks or flattened sections collect grime and emit foul smells. Gaskets are inexpensive and easy to swap.
• Drain hose: Kinks, low spots (“sags”), or sludge buildup cause stagnant water. Shorten or reroute for a smooth, high-loop path.
• Air gap (if fitted): Remove the cap at the sink, clean any sludge, and reseat it.
• Check valve: A stuck valve allows backflow. If odors return quickly after cleaning, this is a suspect.
• Heater shield & lower panel: On some models, a small shield near the element can trap melted plastic or crumbs.

Installation & plumbing essentials (small details, big impact)

• High loop or air gap: The drain hose must arc up and attach under the countertop before dropping to the disposal or tailpiece. This prevents sink water from siphoning into your dishwasher.
• Garbage disposal knockout plug: If the dishwasher was newly connected and won’t drain—or smells foul—the knockout plug inside the disposal inlet might still be in place.
• Sink habits: Always run the disposal with cold water for 30 seconds before starting the dishwasher to clear the path.
• Trap & venting: Chronic sewer smells may indicate a dry P-trap or venting issue at the sink, not the dishwasher itself.

Daily and weekly habits that prevent odors

• Scrape, don’t pre-rinse: Modern detergents need a bit of soil to activate, but avoid large chunks that clog filters.
• Load so the spray can reach everything: Nesting bowls or blocked utensil baskets shelter food bits.
• Use the hottest appropriate cycle weekly: Heat kills odor-causing bacteria and dissolves fats.
• Detergent discipline: Use fresh, high-quality detergent and the recommended amount—too much creates residue, too little leaves grease.
• Rinse aid helps: It speeds drying, which discourages musty smells.
• Door ajar after cycles: Let steam escape so the tub dries out.
• Monthly cleaner: Run a machine cleaner or vinegar cycle once a month, more often in hard-water areas.
• Clean the filter: Quick rinse weekly; deep clean monthly.

Troubleshooting quick table

Symptom	Likely Cause	Fast Fix
Sour, stale odor	Dirty filter & sump	Remove/clean filter; vinegar cycle
Rotten-egg smell	Backflow from sink/disposal	Clear disposal; add high loop/air gap
Musty/slimy	Biofilm on gasket & walls	Scrub folds; run sanitize or cleaner
Fishy	Protein residue	Clean spray arms; hot enzyme cycle
Burning/plastic	Melted utensil or element issue	Remove plastic; if it persists, stop and consult a pro

When DIY isn’t enough

If you’ve cleaned thoroughly, confirmed the high loop/air gap, and the smell returns within a few washes, you may be dealing with a faulty check valve, persistent drain-hose contamination, or a plumbing vent issue. At that point, document what you’ve tried (photos help) and consult the dishwasher manufacturer or a licensed local technician.

Remember, Appliance Rescue focuses on expert guides, appliance tips, and troubleshooting advice—not repair services. For questions about this article or to request a topic we should cover next, feel free to Contact us.

Final Tip

A smelly dishwasher is rarely “broken”—it’s usually a cleanliness or drainage detail. Tackle the filter and sump first, confirm the drain setup, and make hot, regular cleaning part of your routine. Your nose will know when you’ve won.