A litter box that smells the moment you walk into the room is common, and it rarely has a single cause. Odour usually comes from a combination of the waste itself, how often the tray is cleaned, the litter and how much of it is used, where the box sits, and sometimes your cat's diet, stress levels or health. Here's how each one contributes, and what you can do about it.
Cause 1: Urine and faeces breaking down
The sharp smell most people associate with a dirty litter box is largely ammonia, which forms as bacteria break down urea in urine. Faeces add their own odour. The longer waste sits in the tray, the more time there is for that breakdown to happen, which is why the smell often builds through the day.
What helps: remove waste promptly (see Cause 2), and choose a litter designed to help manage odour rather than simply mask it with fragrance.
Cause 2: Cleaning frequency
Even a litter that clumps well can't help much if clumps stay in the tray for days. Waste keeps producing odour for as long as it's there.
What helps: scoop at least once a day, and more often if several cats share a tray. Top up with fresh litter as needed, and every so often empty the tray completely, wash it with warm water and a mild, unscented detergent, dry it, and refill. Strong-smelling cleaning products can put some cats off the tray.
Cause 3: The litter itself, and how much you use
Some litters rely on fragrance to cover odour, which can fade after a while. Others don't clump or absorb well, so moisture stays near the surface. Using too little litter can also be a problem: urine can reach the bottom of the tray, where it's harder to remove.
What helps: use a clumping litter that forms firm clumps you can lift out cleanly, and keep the litter deep enough that clumps form within the litter rather than sticking to the tray base. Check your litter's packaging for its recommended depth. Enzyme-based litters are one approach to odour control: our Original and Plus formulas include enzymes intended to help break down odour at the source instead of masking it with fragrance, and Plus is a dual-enzyme formula designed for multi-cat households. How well any litter controls odour still depends on the other factors in this article, especially cleaning frequency and the number of cats per tray.
Cause 4: Ventilation, placement and number of boxes
A box tucked into a small, closed-in space traps odour. In multi-cat homes, sharing one tray means a much higher load of waste per box, and some cats will avoid a tray that already smells strongly.
What helps: a common guideline is one litter box per cat plus one extra. Put boxes in quiet, well-ventilated spots, away from food and water bowls.
Cause 5: Diet and stress
A change of food can change how your cat's waste smells, and some diets produce stronger-smelling stools than others. Stress, such as a house move, a new pet or changes to routine, can also change toileting habits, including where and how often your cat goes.
What helps: make diet changes gradually, and talk to your vet before changing your cat's diet to deal with odour. Keep routines as steady as you can, especially around the litter box.
Cause 6: Health issues
Sometimes a change in smell is a sign that something is wrong with your cat rather than the litter box. Urinary problems, digestive upsets and other health conditions can change how urine or faeces smell, and how often your cat uses the tray.
When to see a vet
This article is general information, not veterinary advice, and no litter is a treatment for a health problem. Get your cat checked by a vet promptly if you notice any of these:
- a persistent or sudden change in how the litter box smells
- straining in the tray
- blood in the urine or stool
- repeated or unusually frequent trips to the tray
- signs of pain when using the tray
- new avoidance of the tray
- passing little or no urine
A cat that can't pass urine is an emergency. Contact your vet or an emergency vet straight away.
Putting it together
Persistent litter box smell is usually a combination of causes. Infrequent scooping, not enough litter, and too few boxes for the number of cats often come up together. Working through them one at a time usually makes a noticeable difference.