1. A Naturally Damp Environment

The door seal is designed to keep water locked inside the drum during a wash. The downside is that these airtight seals trap moisture and don’t naturally dry out when the door is closed. The folds of the rubber stay damp for long periods, creating the perfect conditions for mould to grow.

2. Biofilm Buildup

Mould doesn’t grow on clean rubber – it anchors into biofilm, a sticky layer of detergent residue, fabric softener, body oils, and organic matter from your clothes. This biofilm collects in the folds of the seal and feeds mould growth. It’s the underlying cause behind most smelly washing machines.

3. Low-Temperature Washing

Modern washing habits favour cooler washes to save energy. While that’s good for your energy bill, low temperatures don’t break down detergent residue or kill bacteria. Over time, that residue builds into biofilm and mould takes hold. Machines that never run a hot wash are far more prone to mould.

4. Too Much Detergent and Softener

Over-dosing detergent and fabric softener leaves residue that doesn’t rinse away fully. This excess builds up in the seal folds, drum, and detergent drawer, feeding mould growth. More detergent doesn’t mean cleaner clothes – it often means more residue and more mould.

5. Leaving the Door Closed

Closing the door straight after a wash traps moisture inside with no way to escape. The seal stays wet and mould thrives. This is one of the biggest contributing factors – and one of the easiest to avoid.

The cupboard door stays closed

With a machine out in the open, you can leave the door ajar to air out. But integrated machines – and even some freestanding machines fitted into a cupboard space – are hidden behind a kitchen unit door. People naturally close the cupboard door for a tidy kitchen, which means the washing machine door usually gets closed too. The seal never gets a chance to dry, and mould develops far more quickly.

Tip for cupboard-fitted machines: Get into the habit of leaving both the washing machine door and the cupboard door open for a few hours after each wash to let the seal dry properly. It makes a real difference to how quickly mould develops.

Early surface mould – maybe

If you catch it very early, when it’s just light surface specks, a wipe with a mould cleaner and a hot maintenance wash might shift it. The key is catching it before it penetrates the rubber.

Established mould – replacement only

Once mould has worked its way into the folds and penetrated the rubber – which is what we usually see – no amount of cleaning will remove it. The staining and growth are embedded in the material. At this point, the only real fix is a new door seal.

Why cleaning fails on established mould: The rubber is porous, and once mould has rooted into it, surface cleaning only removes what you can see. The mould comes back quickly because it’s living within the material itself. Replacing the seal is the only way to fully solve it.

Leave the door open after use

The single most important habit. Leaving the door ajar after each wash lets air circulate and the seal dry out, stopping mould before it starts. For integrated machines, leave the cupboard door open too.

Run occasional hot washes

If you mainly wash at low temperatures, run a hot wash (60°C or higher) every week or two. Hot water breaks down the detergent residue and biofilm that mould feeds on, and helps keep the machine fresh.

Use the drum clean program

Many machines have a dedicated drum clean or maintenance wash program. Run it regularly – usually monthly – to flush out residue and keep the interior clean. Check your manual to see if your machine has one.

Don’t over-dose detergent

Use the correct amount of detergent – usually much less than people expect. Excess detergent and fabric softener leave residue that feeds mould. Wipe the seal dry after a wash if you can, paying attention to the folds.

The golden rule: Air, heat, and the right amount of detergent. Keep the seal dry between washes, run regular hot cycles, and go easy on the detergent. Do these three things and you’ll give the seal every chance of staying mould-free.