Cat Litter Tray Odour: Causes and Simple Fixes
By Ferplast U.K. | Published: 2026-10-13
Category: Tips & Care
Work out why the tray smells before you scrub it again. A symptom-by-symptom diagnosis of cat litter tray odour, with fixes that actually hold.
Quick answer
Most cat litter tray odour comes from urine sitting in scratched plastic rather than from the litter itself. Scoop solids and clumps at least twice a day, wash the tray weekly with a mild, unscented soap, and replace any tray whose base feels rough or chalky to the touch. If the smell returns within a day of a full clean, the tray is holding odour in its scratches and a replacement will fix it faster than another deep clean.
Match the smell to the cause
Ammonia — that sharp, stinging note — points to urine. It gets stronger when urine has soaked into the plastic or when clumps are left in the tray long enough to break down. A sour, almost cheesy smell usually means the litter itself is saturated and needs a full change rather than another scoop. A musty, damp smell with no obvious wet patch often comes from a hood or a liner trapping humid air, especially in a small bathroom or utility room where there is no airflow.
- Sharp and eye-watering: urine, likely in the plastic or left too long between scoops.
- Sour or stale: litter past its useful life, even if it looks dry on top.
- Damp and musty: poor ventilation, often under a hood or behind a closed door.
- Smell only near the tray, not across the room: usually a cleaning routine problem, not a tray problem.
Build a cleaning routine that holds
Scoop twice a day, morning and evening, and take clumps out the moment you notice them rather than waiting for a set time. Top up the litter to the depth your cat actually digs in — too shallow and urine reaches the plastic, too deep and you waste litter replacing what you throw out with the clumps. Once a week, empty the tray completely, wash it with warm water and a mild unscented soap, and let it dry fully before refilling. Skip ammonia-based or heavily perfumed cleaners: the residue can put a cat off the tray, and a cat avoiding the tray creates a worse odour problem than the one you were solving.
When the tray itself is the problem
Plastic is porous at a microscopic level, and every scoop and scratch opens it a little further. Run a finger along the base and sides: if it feels rough, pitted or chalky even after washing, the tray is holding odour no routine will shift. A deep clean buys you a few days at best. Replacing the tray is the honest fix, and it is usually cheaper than the extra litter and cleaner you would burn through trying to compensate. If you use a hood, check whether the smell is worse inside it than outside — if so, the hood is trapping air rather than the tray failing.
Outdoor access changes the maths
If your cat goes outside, you may find the indoor tray is used less often but smells more sharply when it is used, because waste sits longer between visits. That is a routine problem, not a tray problem: check it daily rather than twice weekly, and do not assume an unused-looking tray is a clean one. Cats that toilet outdoors and indoors also track in damp grit and soil, which adds its own musty note to the tray area.
Odour diagnosis: symptom, cause, action, stopping point
- Ammonia smell returns within 24 hours of a full wash: Urine has soaked into scratched plastic. Wash and dry the tray as normal, then refill. If the smell is back the next day, the plastic is holding it. Stop cleaning and replace the tray. Further washing will not reach the odour.
- Smell is worse inside a hooded tray than outside it: The hood is trapping humid air and concentrating the smell. Remove the hood for a week and see whether the room smell drops. If it does, the issue is ventilation, not your cleaning. Keep the hood off or move the tray to a better-aired spot.
- Tray is barely used but smells strongly when it is: Your cat toilets outdoors most of the time, so waste sits in the tray for days between visits. Check it daily instead of on a weekly schedule. If daily checks are impractical, an outdoor route such as a microchip-reading flap may suit your cat better than an indoor tray.
- Cat is avoiding the tray or toileting beside it: This is no longer an odour problem. A cat that avoids the tray may be reacting to a scented cleaner, a liner, a hood, or discomfort. Stop treating the smell and address the avoidance: unscented cleaning, no liner, hood off, and a vet check if it continues.
Useful kit for the routine
- Hygienic bags PA 6720: Hygienic bags PA 6720 are resistant nylon bags supplied as two rolls of 40 pieces, designed to collect droppings without dirtying your hands, and they fit Ferplast hygienic bag holders such as PA 6722, PA 6724 and Dudù. Having bags within reach at the tray is what makes twice-daily scooping realistic rather than aspirational; a bag you have to hunt for is the reason most routines slip by day three.
- NIPPY: Nippy is a plastic poop scoop that folds small enough for a pocket or handbag, opens with a click, and takes a hygienic bag before you collect droppings. If the tray sits near a door or you empty waste straight into an outdoor bin, a folding scoop keeps the job quick and keeps your hands clear of the tray.
- SWING MICROCHIP LARGE: Swing Microchip Large is an electronic cat flap for large cats and small dogs with an antenna that reads the microchip under your pet's skin, so only your own animal can pass through. It is available in a choice of colours. A microchip-reading flap lets your cat reach an outdoor toilet area without leaving the house open to neighbourhood cats, which is often the real source of a smell you have been blaming on the tray.
