On a damp Tuesday evening, while the kettle hummed and the rain stitched silver threads across the kitchen window, I discovered that my washing machine had been lying to me. It looked clean. It smelled almost clean. It whirred dutifully through its cycles, folding hours into the spin of a stainless-steel drum. But there, under the rubber lip of the door, hiding like a secret in the folds of a story, was a slick, dark smear of mould—quietly colonizing the place I trusted to clean everything else I owned.
The tiny white dot that changes how you see your washing machine
The discovery started with something that looked almost too silly to matter: a dot of toothpaste. Not a fancy cleaning product. Not a specialist mould spray. Just the same faintly minty paste lined up on your bathroom sink.
A friend had mentioned it in passing, over coffee, like a strange campfire story for adults who own appliances. “If you really want to know if your washing machine has hidden mould,” she said, “do the toothpaste dot test.” She shrugged. “Tonight. You’ll see.”
I almost laughed it off. But that night, as the rain kept falling and the house was filled with the muggy breath of drying clothes, I remembered her words. So I padded over to the laundry corner, opened the machine door, and pressed a tiny pea-sized dot of white toothpaste onto the inside of the rubber door seal—the grey gasket that folds back like a thick, tired eyelid.
It felt almost like leaving a note for the machine. A little message that said, “I’m watching you.” Then I closed the door and set a hot wash with no clothes, just an empty cycle roaring around that lonely, minty dot.
When the cycle finally clicked to an end, the door sizzled faintly with trapped heat. I pulled it open and reached for the gasket. What I saw didn’t look like the gleaming, rinsed-clean finish I had expected. Instead, the toothpaste that remained had turned a faint brown-grey at the edges, its once-bright white now muddied—as if it had dragged up something from the folds of that rubber lip, something I couldn’t see before.
I peeled back the gasket, and that was when the truth arrived: small, peppery flecks of black, streaks of slime-darkened rubber, and that unmistakable damp smell—a smell you don’t notice until you really inhale, and then you can’t ignore.
My washing machine, the faithful workhorse of daily life, was a quiet mould factory.
What the “toothpaste dot” test actually reveals
The charm of the toothpaste dot test is how disarmingly simple it is. No kits. No test strips. No lab coat. Just a paste we trust to clean one of the most intimate places on our body—our mouths—used as a tiny white flag in the hidden war inside the machine.
Here’s how it works in practice, if you want to try it tonight:
- Choose a small dot of plain white toothpaste (not gel, not colored, no exfoliating beads).
- With dry fingers, pull back the inner rim of your washing machine door seal—the rubber gasket.
- Press that dot into one of the folds, ideally where water usually sits after a wash.
- Close the door and run an empty hot cycle (60°C or higher if your machine allows).
- When the cycle is over, open the door, peel back the seal, and look at the toothpaste.
If the dot is still mostly white, just a little smudged, your machine is probably in decent shape. But if it’s streaked with brown, grey, or tiny black specks, or if it has taken on a murky tint, it has done something revealing: your toothpaste has become a tiny trap for grime, biofilm, and microscopic mould particles shaken loose during the wash.
Toothpaste is mildly abrasive and sticky enough to hang onto particles that would otherwise slip past your eye. It clings to the dirt that your regular laundry cycles don’t quite manage to rinse away. In a way, it’s like dusting a surface with powder to reveal fingerprints—only here the prints belong to the slow, quiet life of mould and bacteria.
The result isn’t a lab diagnosis; it’s a story. A story your machine is finally willing to tell you, once you ask the right question in the right language—mint, chalk, and water.
The hidden ecosystem inside your washing machine
If this all sounds a bit dramatic, consider what a modern washing machine really is: a warm, moist, nutrient-sprinkled cave. We stuff it with clothes flecked with skin cells, sweat, oils, and food. We add detergent and, often, fabric softener. Then, when the spinning stops, we often slam the door shut and walk away, trapping in the moist air.
To mould, this is paradise. A pocket forest waiting to happen.
The rubber door seal is one of mould’s favorite neighborhoods. It’s soft, textured, and always just a little bit damp, especially if water pools at the bottom lip. The detergent drawer is another: a sticky, half-flushed canal where trickles of soap cling to plastic corners. And behind the drum—where we can’t see—lie the stubborn films of residue that build over months of low-temperature washes.
You might not see any of this at first. Your clothes might smell “mostly okay.” Maybe, sometimes, they come out with a faint musty tang that you blame on the weather, or the clothesline, or the room you dry them in. Maybe you notice a shadowy ring on the seal and think, I’ll get to that one day.
The toothpaste dot doesn’t create the problem; it just makes the invisible visible. It’s a spotlight in a cave you’ve always walked through in the dark.
| Sign | What It May Mean |
|---|---|
| Clothes smell musty even after drying | Mould or bacterial film inside the drum or seal |
| Visible black spots on rubber gasket | Established mould colony in the seal folds |
| Detergent drawer has slime or residue | Soap build-up feeding bacteria and mould |
| Cloudy door glass after washes | Detergent film and microscopic debris not rinsed away |
| Toothpaste dot turns grey or speckled | Hidden grime or mould particles dislodged during the cycle |
Turning the test into a nighttime ritual of rescue
There is something quietly satisfying about reclaiming a neglected corner of your home. Once you’ve seen what the toothpaste dot reveals, the next steps feel less like chores and more like a small, determined rescue mission.
You don’t need to tear your machine apart. You just need to move slowly, paying attention to the places water loves to linger and dirt loves to hide. The same way you might gently untangle a riverbank after a winter flood, you can begin to unpick the mould’s hold on your machine.
Here’s one way to handle it, step by step, in the same evening you run the test:
- Unplug the machine. The magic of domestic heroics is always safer without electricity humming in the background.
- Peel back the gasket. Use an old cloth dipped in warm water and a mild cleaning solution (or diluted white vinegar if your manufacturer allows it). Swipe slowly along the folds, turning the cloth as it darkens.
- Visit the detergent drawer. Slide it out as far as it will go; many can be fully removed with a small upward tug. Soak it in warm water, scrub off the clinging soap, and wipe the slot where it usually lives.
- Run a maintenance wash. After the hand cleaning, run another hot cycle—this time with a machine cleaner or, if recommended for your model, a cup of white vinegar or washing soda in the drum.
- Let it breathe. When the cycle ends, leave the door open. Let the warm, ghostly air drift out. Mould loves the stale stillness of a closed door; it hates time and air and dryness.
You may find, in the quiet of this small mission, that you feel oddly protective of this humming appliance you’ve mostly taken for granted. You scrub the rubber folds like you might clean mud from a child’s boots after a long day outside. You feel the satisfaction of wringing blackened water out of the cloth, proof that something has been set right.
And just like that, the toothpaste dot becomes more than a trick; it becomes the beginning of a new relationship with an everyday machine.
How mould quietly follows you off the spin cycle
Hidden mould in a washing machine doesn’t stay politely where it started. It travels. It hitchhikes in threads and fibers, in the invisible film that clings to towels, socks, and pillowcases. You might not always see the stains, but sometimes you’ll recognize the signs:
- That towel you just washed twice still smells like a closed-up tent.
- The gym shirt you hang up to dry comes back with a faint “wet basement” note.
- You notice your black clothes, especially, hold on to a strange, stale scent.
In a way, it’s like bringing forest floor mud back on your boots long after you’ve left the trail. The spores move, whether you invite them or not.
This is not a call to panic, but a nudge toward awareness. If someone in your home has allergies, asthma, or a sensitive nose, that hidden mould load could be quietly irritating them. Even if you’re all healthy, there’s something slightly heartbreaking about bathing, dressing, and sleeping in fabrics that never quite feel crisp and clean, no matter how many detergent pods you sacrifice to the cause.
The toothpaste dot test doesn’t just reveal mould; it reveals the quality of the rinse your life has been passing through every week. Once you know that, it’s hard to un-know it—and that’s a powerful thing. Awareness is the first small rebellion against letting your home run on autopilot, slowly sliding towards “good enough” when what you really want is “actually clean.”
Keeping the machine wild-clean, not wild-dirty
Nobody wants a clinical, sterile home. We track in mud from gardens, sand from beaches, pine needles from walks. Our clothes remember where we were—the café, the bus, the park path, the crowded train. Life leaves a residue, and that’s part of its charm.
But there’s a difference between the honest dirt of living and the stagnant grime of neglect. One tells stories; the other slowly eats away at the edges of comfort.
Think of your washing machine as a small, domesticated river. You don’t want it chlorinated into oblivion, but you do want the water to run clear. A few small habits can keep it more stream than swamp:
- Open the door after every wash. Let the drum and seal dry out between cycles.
- Use the right amount of detergent. Too much creates film; more soap isn’t more clean.
- Skip fabric softener sometimes. It can leave a waxy, mould-friendly residue.
- Run a hot maintenance wash monthly. Especially if most of your laundry is done on cool, eco-friendly cycles.
- Check the filter. If your machine has one, clear it of lint, coins, and the small artifacts of daily life.
The toothpaste dot test can become a recurring little check-in—once every few months, perhaps. A tiny white marker at the edge of your domestic river, letting you know whether the water still runs clear or is quietly clouding again.
Frequently Asked Questions
Does the type of toothpaste matter for the dot test?
Yes, it’s best to use plain white toothpaste without added colors, microbeads, or gel formulas. The simple abrasive paste makes it easier to spot discoloration and trapped grime after the cycle.
Is the toothpaste dot test safe for my washing machine?
In the tiny amount used, it is generally safe. Apply only a small pea-sized dot to the rubber seal, not to internal components or electronic parts. The residue will rinse away during the cycle, just as detergent does.
What if my toothpaste dot stays clean and white?
That’s a good sign. It suggests your gasket and wash water aren’t heavily contaminated with visible grime or mould particles. Still, routine cleaning and occasional hot maintenance washes are recommended to keep it that way.
Can I rely on this test to detect all mould in my machine?
No. The toothpaste dot test is an informal visual indicator, not a scientific measurement. It can reveal hidden grime and suggest mould presence, but mould can still exist in places the dot doesn’t reach, like deep behind the drum or in hoses.
My machine smells musty but the dot looked clean. What should I do?
Odor can come from other areas, such as the drain filter, detergent drawer, or internal hoses. Clean the drawer thoroughly, check the filter, run a hot maintenance cycle, and leave the door open between washes. You can repeat the dot test in a different area of the gasket next time.
How often should I repeat the toothpaste dot test?
Every few months is enough for most households, or after a period of heavy use such as washing lots of towels, sports gear, or pet bedding. Use it as a spot-check, not a daily ritual.
What if I find heavy mould on the seal?
If the mould is extensive, thick, or crumbling, you may need to replace the gasket entirely. For moderate build-up, careful cleaning with a suitable cleaner can help, but always follow your machine manufacturer’s guidelines to avoid damage.
Will cleaning my machine once solve the problem for good?
It will improve things, often dramatically, but mould and residue can return if the conditions stay favorable—cool washes, excess detergent, and a tightly closed door. Ongoing small habits are the key to keeping your machine clear.
Can hidden mould affect my health?
For many people it may only cause unpleasant odors, but for those with allergies, asthma, or sensitivities, mould exposure can contribute to irritation and respiratory discomfort. It’s worth taking seriously, especially in a machine that cleans fabrics you wear and sleep in.
Is this test useful for top-loading machines?
Top-load washers often have different seal setups, so the exact spot for a toothpaste dot may vary. You can try placing a tiny dot on a frequently damp rubber edge inside the lid area, but the results may be less obvious than with front-load gaskets. Regardless, regular cleaning and an open lid after washes are still important.
Hello, I’m Mathew, and I write articles about useful Home Tricks: simple solutions, saving time and useful for every day.
