Last Updated on October 4, 2026 by Umar Farooq
If your washing machine smells musty, the smell itself is most of the diagnosis — a damp, mildewy smell means biofilm growing inside the machine, and that is a different fault from sewer gas, from stagnant water, and from anything that smells hot. Nearly every page on this subject treats washer odour as one problem with one fix. It is at least four problems, they sit in four different places, and the routine everybody recommends first only solves one of them.
So this is not the cleaning guide. It is the part that comes before it: working out which of the four you have, using your nose and an hour of doing nothing. Get that wrong and you can scrub a gasket to a shine, run three tub-clean cycles, and still have a laundry room that smells — because the smell was never in the machine.
Start with the test that separates the machine from the plumbing
One observation splits the four causes into two pairs, and it costs nothing but patience. Switch the machine off at the wall, open the door as far as it goes, and pull the detergent drawer out to its stop. Then leave the room for an hour. When you come back, smell the laundry room from the doorway before you go near the machine — that first breath is the one that tells you something.
If the smell has faded, it was inside the machine: trapped air in a sealed drum, now vented. If it is as strong with the door standing open, or stronger, the machine is not producing it, and no tub cleaner will touch it. Two minutes of setup, an hour of waiting, and half the advice on this topic is eliminated.
| What it smells like | Where it actually is | The tell |
|---|---|---|
| Musty, damp, mildewy | Biofilm in the gasket, drum ribs and dispenser | Worst after the door has been shut; on the clothes too |
| Sewer, drains, rotten eggs | The standpipe or its trap — not the machine | Present with the machine off and the door open |
| Stagnant, sour, swampy | Standing water in the pump filter or a sagging drain hose | Strongest right at the filter door, near the floor |
| Burning, hot, electrical | Not a smell this page covers | Stop-use — see washing machine burning smell |
Musty and damp: biofilm in the gasket, drum and dispenser
This is the classic one, and the only one that deserves the word musty. What you are smelling is biofilm — a slimy grey-brown layer of bacteria, mould and soap scum that colonises every surface inside a machine that stays damp and dark between washes. It is not dirt in the ordinary sense and it does not rinse away, which is why a normal wash passes straight over it.
Samsung says as much on its own mould page: “When moisture or other residue (such as leftover detergent or other additives) is trapped in a dark place, it may promote the growth of mold and mildew and may cause unpleasant odors” (Samsung washing machine has a mildew smell or visible mold). Three ingredients, all of them normal: water, residue, darkness. A front-loader with the door shut supplies all three, daily, unasked.
The tell is timing. Biofilm smell is worst when you open a door that has been shut for a day or two, it fades within minutes of the door opening, and transfers to whatever you wash next. Three places hold nearly all of it:
- The gasket fold, on front-loaders — pull the lip back and look underneath, not at the face of it (gasket procedure).
- The detergent drawer and its cavity, especially behind the softener siphon, where undiluted product sits and turns to jelly.
- The drum ribs and the space behind them, which you can rarely see and cannot reach — what a maintenance cycle exists for.
Sewer or rotten eggs: this one is not your washing machine
If the smell reads as drains rather than damp — sewer gas, rotten eggs, something faintly chemical — the machine is very likely innocent, and the door-open test will have told you so already. Your drain hose empties into a standpipe, and under it there should be a P-trap holding a plug of water. That plug is the only thing between your laundry room and the sewer, and it works passively — another way of saying nobody checks it.
Traps dry out. A machine used once a fortnight, a laundry room in a cold garage, a spell away from home — any of these drops the water level far enough to break the seal. The other version is a partial blockage in the standpipe, where wash water backs up and sits. Pour a couple of gallons down it: if the smell goes within a day, it was a dry trap. If the water backs up while you pour, washing machine drain pipe overflowing is your page.
Stagnant and sour: water standing where it should not be
The third smell is different again — sour, swampy, closer to a vase of week-old flowers than to mildew — and it comes from water that never left. On front-loaders and combo units, the drain pump filter behind that small door at the bottom holds a little water permanently by design, along with whatever it has strained out of the last two hundred washes. If the smell is strongest when you crouch at the front rather than at the open door, that is your answer.
The drain hose is the other reservoir, carrying a cause almost nobody mentions. LG’s instructions keep the hose end close to its elbow bracket for a reason unrelated to leaks: “If the drain hose is extended more than 4 inches beyond the end of the elbow bracket, mold or microorganisms could spread in to the inside of the washer” (LG drain hose installation). A hose pushed too deep, or sagging in a loop, holds standing dirty water with a path back to your drum (washing machine drains too slowly).
Burning, hot or electrical: stop
Switch the machine off at the breaker, not at the plug. Do not run another cycle to see whether the smell comes back.
A hot, burning or electrical-plastic smell is not a cleaning problem and does not belong on this page. Go to washing machine burning smell instead.
Why your washing machine smells musty in the first place
None of this means you are doing laundry wrong. A modern machine washes in a fraction of the water its predecessors used, mostly at low temperatures, inside a sealed drum behind a rubber seal, then sits with the door shut until the next load. That is an efficient washing machine, and it is also, unavoidably, a warm damp box. The design that saves the water is the same design that grows the biofilm.
What varies between households is how much food the biofilm gets, and that is almost entirely detergent. Surplus detergent and softener do not vanish at the end of a cycle — they coat the drum, the drawer and the gasket, and they are the residue Samsung names above. Your dose is the biggest lever you have over how a machine smells, bigger than any cleaning product: read signs of too much detergent, correct the amount at how much detergent to use, and check the type at HE vs regular detergent.
Clearing it, in the order that works
Order matters, because most people run the cleaning cycle first and are quietly disappointed. A maintenance cycle circulates hot water through the drum; it does not scrub a gasket fold, empty the pump filter, or straighten a sagging hose. Do the physical removal first, then run the cycle for what you could not reach.
- Run the door-open test above and confirm the smell is in the machine.
- Clean the gasket fold and the detergent drawer by hand — gasket procedure here.
- Empty and rinse the drain pump filter, and straighten the hose behind the machine.
- Then run a hot maintenance cycle — washer tub clean cycle explained.
- Keep the door and drawer ajar between washes, and fix the detergent dose.
For frequency, Samsung puts a number on it rather than leaving it vague, and it is worth borrowing: “The Self Clean reminder LED will display after 20 washes on a top load model or 40 washes on a front load model” (Samsung — how to clean your washer). That is a useful benchmark on a machine wearing any badge. The full routine is at how to deep clean a washing machine; if a Samsung reminder will not clear, Samsung Self Clean light stays on covers it.
FAQ
My washing machine smells musty but my clothes come out fine. Why?
Biofilm in the gasket and drawer sits outside the water path, so a load can pass through without picking much of it up. It is still worth clearing: it only goes one way from here. If the clothes smell and the machine seems fine, that is a different problem — see clothes smell after washing.
Why does my washer smell like rotten eggs rather than mildew?
That is sewer gas, and it usually means the P-trap under your standpipe has lost its water seal, or the standpipe is partly blocked. Confirm it with the door-open test: a smell unchanged with the machine off and open is not from the machine.
Does leaving the door open between washes actually help?
Yes, and it is the highest-value habit on this page. Samsung’s own guidance is to “Leave the lid or door open to let the washing machine dry. Also leave the detergent drawer open to help it dry as well.” Drying the drum removes one of the three things biofilm needs.
Will vinegar or bleach get rid of the smell?
They kill some of what they touch, and that is the catch — neither reaches into a gasket fold or behind the drum ribs, so the smell returns. Manufacturers also differ on what they will sanction in a drum, so check your own manual before either becomes routine. Physical removal first, product second, never mixed.
Do top-loaders get musty too, or is it only front-loaders?
Front-loaders are far more prone to it, thanks to the sealed gasket and the low water volume. Top-loaders are not immune — the dispenser, the underside of the lid and the outer tub all hold residue. Samsung’s shorter reminder interval for top-loaders, 20 washes against 40, suggests they are not being ignored.
How long before the smell comes back?
If you removed the source and corrected the dose, months. If it returns within two or three washes, you missed some of it or something is still holding water — check the pump filter and the drain hose before repeating the cycle.
A maintenance signal, not a fault
A musty machine is not a machine going wrong. It is a machine doing what a warm, damp, sealed box does, and the smell is a maintenance signal rather than a fault. The useful move is not buying a cleaner — it is working out which of the four smells you actually have, because three of them are not fixed by cleaning the drum.
The one smell that does not belong anywhere on that scale is the hot one. That is not maintenance, and it does not wait for the weekend.
