Ammonia smell from cloth nappies almost always means a build-up problem, not a nappy problem, and it's fixable within one wash cycle in most UK households.
- A hot strip wash at 60°C removes the detergent and mineral build-up that causes ammonia smell in cloth nappies.
- Under-dosing detergent is the number one cause of smelly cloth nappies in 2026 - most parents use too little, not too much.
- Plant-based laundry sheets from Re:gn dissolve fully in the wash, leaving no residue for bacteria to feed on.
- Dry storage between washes beats a wet bucket every time - soaking encourages the exact bacteria that cause odour.
- Fragrance booster beads mask smell short-term, but they don't fix the underlying wash routine - treat them as a finishing touch, not a cure.
Why this matters
A smelly nappy stack is the single biggest reason parents quit cloth nappies in the first three months. It's rarely the fabric - it's usually a wash routine that isn't hot enough, long enough, or dosed with enough detergent to strip out ammonia crystals building in the fibres.
Get the routine right once and the smell problem stays fixed. This guide walks through the fix step by step, plus the mistakes that keep parents stuck in the same cycle.
What you'll need
- A washing machine capable of a 60°C cycle
- A non-bio, plant-based detergent free of fabric softener additives
- A spare bucket or dry pail liner for storing dirty nappies between washes
- Digital or physical kitchen scales if you're weighing detergent doses
- Access to outdoor line-drying or a well-ventilated indoor space
- Your existing stack of reusable cloth nappies with inserts - the fix works on any brand, not just one
The steps
1. Run a strip wash first
A strip wash removes the layers of detergent residue, minerals, and ammonia crystals that build up over weeks of washing at lower temperatures. This is the reset button before any new routine works.
Run nappies through a 60°C cycle with no detergent, then a second 60°C cycle with your normal dose. Expect to see grey, sudsy water on the first rinse - that's the build-up leaving the fabric. Skipping this step is why a new detergent alone rarely fixes existing smell.
Common mistake: stripping at 40°C. Ammonia crystals need heat above 50°C to dissolve properly.
2. Increase your detergent dose
Most parents dose cloth nappies like regular laundry, which under-treats heavily soiled fabric. Nappies need roughly 1.5x a normal load's detergent dose because they're more absorbent and more soiled than an average wash.
Weigh your nappies dry versus wet before adding detergent, and dose against the wet weight, not a guess. A laundry detergent sheet makes this easier because each sheet is a fixed, measured dose - no over-pouring, no under-pouring.
3. Wash at 60°C, not 40°C
Ammonia-producing bacteria thrive at lower wash temperatures. A 60°C main wash, run at least twice a week in 2026, keeps bacterial load from building between cycles.
If your machine's eco cycle defaults to 40°C, override it manually for nappy loads. Expect a full cycle to run 20 to 30 minutes longer at the higher temperature - that's the trade-off for odour control.
Common mistake: relying on a quick 30-minute cycle. Nappies need the full wash length to agitate and rinse properly.
4. Cut the fabric softener completely
Fabric softener coats fibres with a waxy residue that blocks absorbency and traps odour-causing bacteria against the fabric. This is one of the most common reasons a stack that smelled fine at three months starts smelling ammoniac by six.
Switch to a plant-based sheet with no softening agents and let the nappies air-dry to keep them soft naturally.
5. Store dirty nappies dry, not soaking
Wet-pail soaking used to be standard advice, but it encourages the exact anaerobic bacteria that cause the sharpest ammonia smell. A dry pail with a washable liner, emptied every second day, controls smell far better through 2026's typical machine designs, most of which handle dry-pail loads more efficiently than older top-loaders ever did.
Expected outcome: nappies that smell neutral straight out of the pail, not just after washing.
6. Add a scent booster as a finishing step, not a fix
Once the wash routine is solid, a scent booster gives a final freshness lift without masking an underlying problem. Fragrance booster beads added to the final rinse work well here - a small scoop is enough, and more isn't better since excess residue can itself trap bacteria over time.
Common mistake: using booster beads to cover up an unsolved ammonia problem instead of fixing the wash temperature or dose first.
7. Dry outside whenever you can
UV light and fresh air both break down residual bacteria that survive the wash cycle. Line-drying for even two to three hours makes a measurable difference to how nappies smell once dry, even on a cloudy UK day.
Tumble drying is fine occasionally, but it doesn't have the same bacteria-killing effect as sunlight.
Troubleshooting
Nappies smell fine wet but reek once dry. This is classic ammonia crystallisation - the smell only activates on contact with warmth and moisture, like a baby wearing the nappy. Run a strip wash immediately.
Smell returns within two days of a clean wash. Your detergent dose is too low for the soil level, or you're washing at 40°C instead of 60°C. Bump both up before trying anything else.
Nappies have grey or yellow staining alongside the smell. This usually means mineral build-up from hard water combined with bacteria. A natural bleach routine for cloth nappies handles both the staining and the smell in one pass without damaging the fabric's absorbency.
Machine smells musty even when nappies come out fine. The drum itself has build-up. Run an empty hot cycle with no nappies at least once a month.
Booster beads mask the smell for a day, then it's back. Boosters are cosmetic - they don't fix detergent dose or wash temperature. Treat the underlying routine first.
Nappies smell like ammonia specifically overnight. Overnight wear means longer contact time with concentrated urine. Add a booster insert for overnight use and shorten the gap between washes to every second day instead of every third.
Tools and resources
- A laundry detergent sheet dosed correctly against wet nappy weight
- Fragrance booster beads for a final freshness pass, used sparingly
- A dry pail liner, changed every second day rather than left to soak
- Re:gn's dedicated guide to laundry sheets for cloth nappies for dosing specifics by machine type
What to do next
Once the smell problem is solved, the next thing that trips parents up is staining and stiffness after line-drying. Work through the natural bleach routine linked above if grey staining is still visible after two clean strip washes - that's the sign mineral build-up, not bacteria, is the remaining issue in 2026's typical UK hard-water areas.
FAQ
How do I stop cloth nappies smelling of ammonia?
Run a 60°C strip wash with no detergent first, then wash again at 60°C with a full detergent dose. Ammonia crystals need heat above 50°C to dissolve, which is why 40°C washes rarely fix the smell.
Why do my cloth nappies smell fine wet but bad once dry?
That's ammonia crystallisation - residue that only releases odour on contact with warmth and moisture. A strip wash at 60°C clears the crystals from the fabric.
Should I soak dirty cloth nappies before washing?
No - wet-pail soaking encourages the anaerobic bacteria that cause the strongest ammonia smell. Store nappies dry in a lined pail and wash every second day instead.
How much detergent do cloth nappies need?
Roughly 1.5x a standard laundry dose, measured against the wet weight of the nappies rather than a rough guess. Under-dosing is the most common cause of persistent smell.
Does fabric softener make cloth nappies smell worse?
Yes - softener coats fibres with residue that traps bacteria and blocks absorbency. Switch to a plant-based detergent sheet with no softening agents.
How often should I wash cloth nappies to stop smell building up?
At least twice a week at 60°C, with a monthly empty hot cycle to clear machine drum residue. Waiting longer between washes lets bacteria and ammonia crystals build faster than a single wash can remove.
Do scent booster beads actually fix smelly nappies?
They mask smell for a day or two but don't fix detergent dose or wash temperature. Use booster beads as a finishing touch after the wash routine is corrected, not as the main fix.
Can hard water cause cloth nappy smell?
Hard water contributes mineral build-up that combines with bacteria to cause both staining and odour. A natural bleach routine designed for cloth nappies clears both issues together.
One last thing
The detail most parents miss: a strip wash only works if the machine drum itself is clean first. Running a fresh strip wash through a musty drum just redeposits the same residue onto clean nappies, so the empty hot cycle step isn't optional - it's the step that makes everything else in this routine actually stick.
