As soon as the weather turns and you air the house less, you notice it straight away: the cat litter box smells and that odour lingers in the living room. It's almost never the cat's fault, or the litter you buy — it's how often you clean the tray and where it sits. A few changes and the smell is gone within a week, without air fresheners that only mask it.
Why the cat litter box smells
That sharp smell is ammonia. Cat urine contains urea and, as soon as bacteria have time to work on it, they break it down into ammonia. The longer the urine sits in the tray, the stronger it smells. Add to that the most common mistakes:
- Scooping only once a day. For most homes, that isn't enough.
- Not enough litter. Below 5 cm, urine reaches the bottom and ends up soaking into the plastic.
- A covered tray with a lid. It traps the smell until you open it, and plenty of cats find it claustrophobic.
- Too few trays. Two cats sharing a single litter box is asking for trouble.
- An old, scratched tray. The scratches absorb urine and keep smelling however hard you scrub them.
The routine that gets rid of the smell
- Scoop twice a day, morning and night, and not just the solids: the clumps of urine too.
- Top up to 5-7 cm. Every clean takes litter away, and what's left is usually too shallow.
- Empty the whole tray every two to four weeks. Scrub it with hot water and a little unscented neutral soap.
- Don't use bleach or anything containing ammonia. Ammonia smells like another cat's urine and yours will start going outside the tray. Diluted vinegar (1 part to 3 parts water) does work and shifts limescale and urine residue.
- Dry it properly before refilling. Litter poured onto a wet base clumps and starts to smell as soon as you shut the house up.
- Replace the plastic tray every one or two years, or sooner if the base feels rough when you run your hand over it.
Litter, placement and how many trays
Clumping bentonite litter seals urine in quickly and lets you lift it out whole, which is exactly what you want. Silica crystals absorb moisture beautifully but let more faecal odour through. Always choose it unscented: the fragrance evaporates within a day and some cats will refuse a perfumed tray outright.
The rule on numbers is simple: one tray per cat, plus a spare. Two cats, three litter boxes. Spread around different spots, not all three lined up in the same corner.
Put the tray somewhere quiet where the cat doesn't feel watched, but never inside a closed cupboard or a small unventilated room: the smell just sits there. And not next to the food and water bowls either, because plenty of cats eat less with the litter box nearby.
When the smell is a health warning
If the urine suddenly smells much stronger, your cat starts going outside the tray, urinates more often than usual or far less, or you see blood, book an appointment with the vet. Cystitis, kidney problems and diabetes all change the smell and the frequency, and the sooner they're picked up the better. Unneutered males also spray with a particularly pungent odour that no amount of extra cleaning will fix.
If the smell is in the room and not the tray
When the litter box is clean and it still smells, the odour has settled into everything around it: the mat, the skirting board, the floor. Air the room hard and briefly, five or ten minutes with a cross draught, rather than leaving a window ajar all day. Put a washable mat under the tray to catch the litter that comes out stuck to their paws, and wash it weekly. If urine has got onto the laminate or the skirting, use an enzymatic cleaner: it breaks urea down, whereas an ordinary cleaner just spreads it around. And keep air fresheners away from the litter box; mixed with ammonia it smells worse.
One more thing you notice once the house is shut up: hair. If your cat is spending more hours indoors, the sofa and the blankets show it. A reusable lint remover handles the daily once-over without getting through rolls of sticky tape. You can see the rest of our ideas for the home and for pets in the full collection.
In short: scoop twice a day, a 5 to 7 cm layer, unscented litter and one more tray than you have cats. Nine times out of ten, that's all it takes.