That musty smell almost never comes out of the drum. It comes from the rubber door seal, the detergent drawer and the filter, and what sits in all three is detergent that was never rinsed away. Which is why running the machine hot with nothing in it usually changes so little.
Short answer
Wipe out the door seal, take the detergent drawer out, empty the filter, then run the machine empty at sixty degrees with washing powder.
If your washing machine smells, that smell is in the film that collects in those three places. You have to take it out by hand first, because no programme reaches in there. Roughly fifteen minutes of work, and the machine does the rest.
Why a washing machine starts to smell musty
Two habits that both sound sensible are what causes the smell between them.
We now wash almost everything at thirty or forty degrees, and mostly with liquid detergent. That is kind to your energy bill and kind to your clothes. It also means two things are missing from every wash: the heat that dissolves grease, and the bleach, which liquid detergent usually does not contain.
On top of that, nearly everyone uses too much detergent. The cap is generously sized, and more detergent feels more thorough. The opposite is true. Whatever does not get rinsed away stays exactly where it landed.
Those two things together leave a thin, sticky film of detergent residue, grease, fibres and micro-organisms. It settles in the rubber door seal, in the detergent drawer and in the filter, and it holds moisture in all three. That is where the smell is made, and it is why the same machine can smell musty, mouldy or of mildew depending on how long it has been building up. So it comes from both sides at once: from your laundry and from the detergent you washed it with.
That is also why a programme on its own does nothing. Water rinses past those places, not through them.
How to clean a washing machine in five steps
The first three you do by hand and they take about fifteen minutes. The last two the machine does for you.
What follows describes a front loader. A top loader has no rubber seal around a door, so you skip the first step there; everything after it is the same.
- Pull the rubber door seal towards you and wipe it out. Fold the lip back and you can see the underside of it. That is where the dark film sits. Take it off all the way round with a damp cloth, right down into the bottom of the fold, where water stands after every single wash.
- Take the detergent drawer out and rinse it. On most machines there is a small catch at the back that you press in, and then the drawer slides out. Lay it in hot water, not boiling, for ten minutes and the build-up lets go on its own. Wipe out the drawer housing it came from as well, because the same layer is sitting in there.
- Empty the filter. Switch the machine off and pull the plug out. If a programme at sixty degrees or higher has finished not long before, wait half an hour, because the water still in there can be hot. Put a flat dish and a towel under the flap, turn the filter open slowly and only a little way, and let the water come out under control. It can be litres.
- Run the machine empty at at least sixty degrees, with washing powder. The bleach in the powder does the actual work here; heat on its own is not enough. If your machine has a setting called drum clean, use that one and follow the manual. Bosch runs that programme at eighty to ninety degrees, Miele advises at least seventy-five.
- Leave the door ajar afterwards. This is the step that stops the smell coming back, and it costs you nothing at all.
The filter, where the smell actually sits
Hardly anybody opens that little flap at the bottom of the machine by choice.
Everything that gets rinsed out of the drum and cannot get any further collects in the filter: hair, fibres, a coin, scraps of paper. It lies there in a shallow pool of water that never drains away. Warm, damp and dark.
If your machine smells and you have already done the door seal and the drawer, that is where the rest of it is. Expect the first time not to be pleasant.
Do it every three months. It takes five minutes, and in plenty of cases it saves you the phone call to an engineer.
Vinegar or soda crystals: which one should you use?
They do two different jobs, and against this particular smell neither of them does much.
White vinegar
Vinegar is an acid and it dissolves limescale. If you live with hard water and there is white scale on the heating element, that is worth doing. But the smell you are chasing usually has nothing to do with limescale. It comes from soap and grease, and an acid does very little about either. Bosch and Siemens advise against vinegar in the washing machine because of the rubber parts, and Bauknecht allows it only heavily diluted. Against limescale in your kettle vinegar is fine. In the washing machine I would keep it as an exception rather than a routine.
Soda crystals
Soda crystals work from the other direction. They turn grease into a sort of soap, which is why it comes loose faster. That sits much closer to the actual problem. A tablespoon in the drum on an empty programme at sixty degrees can help. Wear gloves while you handle them, because soda crystals irritate the eyes. And mind the difference with bicarbonate of soda: that is sodium bicarbonate, and it is far milder.
Never the two together
Do not mix them, and do not use one shortly after the other either. The two cancel each other out and what you are left with is mostly water with a little salt in it. It becomes genuinely dangerous with chlorine-based cleaners: if those meet vinegar or any other acid, chlorine gas can form, which irritates your eyes and your airways. They do not even have to be in the machine at the same moment for that; shortly after one another is enough. Use one product at a time and rinse the machine through in between.
Why the home remedy stops halfway, and the bottle does too
A home remedy gets you part of the way. The bottle you reach for next runs into the same wall.
On a light film, a home remedy genuinely lifts something away. Once that layer has been sitting there for months, a residue stays behind that will not shift, however long you leave it.
The reflex at that point is to reach for something stronger. That works too, but it meets the very same limit: a liquid stays on the outside. On a sloping surface it runs off, in a grout joint it sinks away, into a fibre it never gets far enough. Which is why you have to repeat it, and why after a year there is a row of bottles under your sink.
Heat works the other way round. Steam goes into the material instead of running across it. It softens what has baked on and it leaves nothing behind that you then have to rinse away again. Only tap water, made hot enough.
And afterwards you still reach for a cloth. That is the one step that comes back in every route.
How to stop it smelling again, with almost no effort
It comes down to three habits, and the first one matters most.
Leave the door and the detergent drawer ajar. A closed drum stays damp for hours after the machine has finished. A gap is enough to let it dry out. This one habit takes the ground out from under the whole problem. If there are small children or pets in the house, keep the door of the room shut instead and put the child lock on, because children and animals can climb into an open drum.
Wipe the door seal dry after the last wash of the day. Ten seconds with a dry cloth. What does not stay standing cannot start to smell. The cloths for that are together under laundry and textile care.
Wash warm once a month. An ordinary wash at sixty degrees counts towards this, so you do not need to run an empty cycle for it. Towels and bedding do that work on their own.
Using less detergent is the actual solution
What never goes in cannot stay behind.
The steps above take out what is already there. But the film builds up in the first place because more detergent goes into the machine than comes back out of it. Dosing is not a detail on the side, it is the cause.
The awkward thing about liquid detergent is how badly it doses. The cap holds more than you need, and the surplus is invisible: you never see where it went. A laundry detergent sheet is pre-dosed for one wash, so there is no estimating involved, and estimating is precisely the moment at which most people take too much. They sit together under laundry detergent sheets.
There is more about that in what laundry detergent sheets are and whether they wash as well.
What you are better off not doing
Two of these tips you will come across everywhere.
Chlorine bleach in the drum. It covers the smell over rather than taking the cause away, and it can leave residues that end up in your next wash. No manufacturer treats a chlorine-based cleaner as a maintenance product for a washing machine. And it must never come into contact with an acid product.
Vinegar every month. Bosch and Siemens advise against it, Bauknecht allows it only heavily diluted. As a standing habit that is not what the manufacturers mean by maintenance.
Skipping the filter because it is disgusting. That is the exact reason it needs doing.
Fabric conditioner as a fix. It masks the smell and it leaves a layer of its own behind, in precisely the place where the problem already is.
Frequently asked questions
Why does my washing machine smell musty or mouldy?
Because a thin film of detergent residue, grease and fibres has built up in the door seal, the detergent drawer and the filter, and that film holds moisture. Washing cool and using too much detergent are what leave it behind: there is no heat to dissolve the grease and, in liquid detergent, usually no bleach either. The smell is made in that damp film, not in the laundry you put in. Take the film out by hand and the smell goes with it.
How often should I clean my washing machine?
Wipe the door seal dry weekly, do the detergent drawer once a month and the filter every three months. An empty run at sixty degrees is only needed if you have not washed anything warm for a while. Those three small jobs together take less time than one big clean-up later on.
Which programme cleans the drum?
If your machine has a setting called drum clean or machine clean, use that one. If it does not, run an ordinary programme at at least sixty degrees with no laundry in it but with washing powder in the drawer. Without detergent there is no bleach in the water and very little happens. Bosch runs its own drum programme at eighty to ninety degrees and Miele advises at least seventy-five, so follow the manual for your model if it has one.
How do I clean the detergent drawer and the housing behind it?
On most machines there is a small catch at the back of the drawer that you press in, and then the whole drawer comes out. Lay it in hot water, not boiling, for ten minutes and the build-up releases on its own. Wipe out the drawer housing it slid out of as well, because the same sticky layer is sitting in there and it is the part people forget. Let both dry before you put the drawer back.
Are those black dots in the door seal mould?
Usually, yes. Moisture stays in the fold of the seal among the detergent residue and the fibres, and mould grows on that. Wipe the fold out thoroughly and the dots disappear. If they sit deep in the rubber and will not come off any more, the rubber itself has been attacked and that will not come out.
I have a top loader, does this apply to me?
In part. A top loader has no rubber seal around a door, so the first step falls away. The detergent drawer and the filter you do have. That filter usually sits behind a flap at the bottom of the front, and on some models on the side instead. Everything else stays the same.
Does vinegar help against the smell in my washing machine?
Usually not. Vinegar is an acid, so it works on limescale, while the smell almost always comes from soap and grease. Bosch and Siemens also advise against using it repeatedly because of the rubber parts, and Bauknecht allows it only heavily diluted. If there is white scale on your heating element and you have hard water, an occasional round is defensible; as a monthly habit it is not.
Why does it fizz when I mix soda crystals and vinegar?
Because the two eat each other up. What is left over is mainly water with a little salt in it, plus water and carbon dioxide gas. That salt cleans practically nothing. So take either vinegar or soda crystals, not both, and rinse the machine through before you switch from one to the other.
What is the difference between soda crystals and bicarbonate of soda?
They are two different substances. Bicarbonate of soda is sodium bicarbonate and it is mild. Soda crystals are sodium carbonate and much fiercer, which is why grease comes loose faster with them. Against the build-up in a washing machine soda crystals are the stronger of the two, but Bosch and Siemens advise against home remedies in the drum in any case.
Can you clean a washing machine with a dishwasher tablet?
That tip does the rounds and it is half right: a dishwasher tablet contains bleach too. But it is made for a different appliance, with a different dose and far more descaler in it. A dose of washing powder does the same work, in the appliance it was designed for, and it costs less.
What is the best product for cleaning a washing machine?
Ordinary washing powder with bleach in it. That is the whole answer. The special washing machine cleaners on the shelf work largely on the same principle at a considerably higher price per run. If your machine has a maintenance programme of its own, follow the manual for your model.
Where is the filter on my washing machine?
On most front loaders it is behind a small flap at the bottom right of the front panel. On some models the flap is at the bottom left, on others it is behind a plinth. Check the manual for your model if you are not sure, and switch the machine off at the plug before you open anything.
It still smells, even though I have done everything
Then the smell is probably not coming from the machine but from the drain. Have a smell at the trap where the drain hose goes in. If it smells the same there, the drain is the source and the machine cannot do anything about it.
Does the smell come from my machine or from my clothes?
If clean laundry already smells musty the moment you take it out of the drum, the problem is in the machine. If it only starts to smell after the washing has been sitting wet in the basket for a while, that is the laundry itself and it needs hanging up sooner.
Elsewhere in the house
Everything is sorted by job under cleaning. And keeping a bathroom dry runs on exactly the same principle as that door seal: what a drying towel actually saves you.