Short answer: a washing machine smells because biofilm grows wherever water sits. Biofilm is body oil, detergent residue, fabric softener and mineral scale bound together by bacteria, and it lives in four places: the door gasket, the drain pump filter, the dispenser drawer and the outer tub behind the drum. Clean those four, run one hot empty cycle a month with citric acid or an oxygen-based cleaner, and leave the door ajar between washes. Total time, about thirty minutes a month.
Why machines start to smell
Three modern habits combine into the problem.
- Cold washing. Cold cycles are right for clothes and for fragrance, but they never get hot enough to clear the oil film that builds on the drum and hoses. Washing cold is not the mistake; washing cold and never running a hot cycle is.
- Fabric softener. Softener is designed to leave a coating behind. Some of it coats the machine: the drawer siphon, the hoses and the outer tub. It is the single most common cause of a mildew smell in a front loader.
- A closed door. A sealed drum with a damp gasket is a warm, dark, humid box. Bacteria need nothing else.
High-efficiency machines use a fraction of the water older ones did, which is good for bills and bad for self-rinsing. Maintenance is now part of the appliance, not an optional extra.
The monthly reset, step by step
- Empty the drum completely. No towels, no "might as well".
- Put 60 ml (a quarter cup) of citric acid, or a dose of oxygen-based machine cleaner, straight into the drum.
- Run the longest, hottest cycle the machine has, or the dedicated tub-clean cycle if it has one.
- While it runs, clean the gasket, the drawer and the filter, as below.
- When it finishes, wipe the drum dry and leave the door open for an hour.
Do not add detergent to this cycle, and never put chlorine bleach in the same cycle as vinegar or citric acid. Mixing acid and chlorine bleach releases chlorine gas. Pick one, and if you use bleach, do it as a separate cycle no more than a few times a year, because it degrades rubber seals.
The door gasket, weekly
On a front loader this is where the smell is. The rubber bellows has a lip that holds a permanent puddle of grey water, hair and lint.
- Fold the lip back with your fingers and look inside. Most people have never done this.
- Wipe it out with a cloth and hot water plus a little washing-up liquid, or a 1:1 white vinegar and water solution.
- Remove hair, coins, receipts and the tissue that went through last month.
- Dry it. Drying is the part that matters; biofilm cannot establish on a dry surface.
- Leave the door ajar after every wash so the gasket can dry on its own.
If the rubber is already blackened, wipe it with a paste of oxygen-based cleaner and leave it for an hour before rinsing. Persistent black staining that will not lift is mould in the rubber itself, and the bellows is a replaceable part.
The drain pump filter, every one to three months
This is the step almost nobody knows exists, and it is the most common cause of a smell like sewage or rotten eggs.
- Find the small hatch at the bottom front of the machine. Lay a towel down and have a shallow dish ready.
- If there is a short drain hose behind the hatch, pull it out, uncap it and let the water empty into the dish first. There can be a litre or more.
- Unscrew the filter cap anticlockwise. Expect standing water and a smell.
- Pull out the filter, clear the debris, and rinse the mesh under a hot tap with a brush.
- Wipe inside the housing, then screw the filter back in firmly and refit the hose and hatch.
Top loaders usually have no accessible pump filter. Older models have a lint trap in or near the agitator instead, which needs the same treatment.
The dispenser drawer, monthly
Pull the drawer fully out, which on most machines means pressing a tab at the back of the softener compartment. Soak it in hot water for ten minutes, then brush the softener siphon and the underside of the drawer housing, where a grey sludge collects. Rinse and refit while wet.
Worth noting: pods go in the drum rather than the drawer, so a household using pods and no softener has a drawer that stays clean by default. The drawer only needs attention if you use liquids or softener.
Top loaders
- No door gasket, so wipe under the lid rim and around the fill opening instead, where splash residue dries.
- Run the hot cycle with citric acid, and if the machine has a tub-clean or sanitise setting, use that.
- Clean the softener dispenser cup on the agitator. It is a common source of smell.
- After the cycle, lift the agitator cap if it removes, and check the shaft for build-up.
- Leave the lid open between washes.
The schedule
| How often | What to do | Time |
|---|---|---|
| Every wash | Remove laundry promptly, leave the door ajar | Seconds |
| Weekly | Wipe and dry the door gasket | 2 minutes |
| Monthly | Hot empty cycle with citric acid, clean the drawer | 10 minutes of work |
| Quarterly | Drain pump filter, deep-clean the drawer housing | 15 minutes |
| Yearly | Check inlet hose screens for grit, inspect hoses for bulges | 15 minutes |
Symptom to cause
| What you notice | Most likely cause | Fix |
|---|---|---|
| Musty or mildew smell in the drum | Wet gasket, door kept closed | Wipe and dry the gasket, leave the door ajar |
| Smell like sewage or rotten eggs | Drain pump filter or trapped standing water | Clean the filter, run a hot cycle |
| Grey flecks or smears on clean laundry | Biofilm shedding from the outer tub | Two hot cycles with citric acid, a week apart |
| White powdery marks on dark clothes | Undissolved detergent or mineral residue | See the hard water guide |
| Clean clothes that smell sour by evening | Load left sitting wet in the drum | Move to the dryer within the hour |
| Everything smells faintly of the machine | No hot cycle in months | Start the monthly reset |
If the smell is in the clothes rather than the machine, the diagnosis runs the other way, and that is covered in why do my clothes still smell after washing.
Five things not to do
- Do not mix chlorine bleach with vinegar or citric acid, ever, in any quantity.
- Do not bleach the gasket weekly. It perishes the rubber and you will be buying a bellows.
- Do not overdose detergent to "keep the machine clean". Excess detergent is what biofilm eats.
- Do not keep using fabric softener while trying to solve a smell. It is usually the cause.
- Do not run the hot cycle with laundry in it and call it maintenance. The cleaner needs an empty drum to reach the tub.
Do you need a dedicated machine cleaner tablet?
No. Tablets are convenient and they work, but what they contain is citric acid or sodium percarbonate, which is oxygen bleach. A 500 g bag of citric acid costs a few dollars and lasts most of a year. Buy the tablets if you prefer the simplicity; buy the acid if you prefer the maths.
Why this matters for fragrance
Perfume cannot survive a contaminated rinse. If the last thing touching your laundry is water that has passed through biofilm, the load will carry that smell underneath whatever fragrance you added, and the two together read as "clean but slightly off". A monthly reset is the least glamorous step in making laundry smell good for weeks, and it is the one that makes the rest work.
The maintenance calendar, printed alongside the fibre index and the care-label decoder, is in The Scent Wash Fabric Care Manual, a free 13-page PDF.
Frequently asked questions
How often should you clean a washing machine?
Run a hot empty cycle with citric acid or an oxygen-based cleaner once a month, wipe the door gasket weekly, and clean the drain pump filter every one to three months. Households that wash mostly cold, use fabric softener or have hard water should stay at the monthly end of every interval.
What is the best thing to clean a washing machine with?
Citric acid for scale and mineral film, or sodium percarbonate, which is oxygen bleach, for biofilm and odour. Both go straight into an empty drum on the hottest cycle. White vinegar works for wiping the gasket and drawer by hand. Never combine any of them with chlorine bleach.
Why does my washing machine smell like rotten eggs?
Almost always the drain pump filter or water standing in the drain path. Open the hatch at the bottom front of the machine, drain the hose into a dish, unscrew the filter, clear the debris and rinse the mesh. Follow it with a hot empty cycle.
Can you use bleach and vinegar together to clean a washing machine?
No. Chlorine bleach and any acid, including vinegar and citric acid, react to release chlorine gas. Use one or the other, in separate cycles, and ventilate the room either way.
Should I leave my washing machine door open?
Yes. Leaving the door and the dispenser drawer ajar between washes lets the gasket and drum dry, and a dry surface cannot grow biofilm. If children or pets are a concern, close it once the drum is dry rather than immediately after the cycle.
Does washing in cold water make the machine smell?
Cold washing alone does not cause a smell, but it does not clear the oil and residue film either. Pair cold everyday washing with one hot empty maintenance cycle a month and the problem does not arise.
