Cat Litter Box Problems: What the Research Actually Shows

This page is not veterinary advice. Paw Multiverse is not a veterinary practice. We cannot examine, diagnose or treat your cat, and nothing here tells you how to treat anything. A cat that has stopped using its tray may be ill, and some of the illnesses behind it are urgent. If your cat is straining in the tray, crying in it, visiting over and over and producing nothing, or if a male cat is trying to pass urine and failing, stop reading and phone your own vet or an emergency vet now. That particular picture is an emergency and it does not wait until morning. Everything below is about what the published record actually says, and it exists to make your conversation with a vet better, never to replace it.

Why this page sits next to our other one

We publish two pages about cats and litter trays and they are deliberately different animals. The household page is the one to read when it happened last night and you want to know what to change today. This is the evidence page. It asks a narrower and less comforting question: for each thing the internet confidently tells you about litter trays, who published it, when, and what kind of study is underneath it.

We split pages this way elsewhere on the site for the same reason. One chocolate page is for the household at the moment of the emergency; the other is for what the published record shows. Advice and evidence are different products and mixing them is how a reader ends up unable to tell a professional consensus from a measured result.

The short version of what follows: the veterinary profession has published a clear, coherent set of recommendations about litter trays; a small number of those recommendations have been tested in controlled conditions; and the single most repeated rule of all, the one about how many trays to own, is the one we could not find a trial for. That last sentence is the most useful thing on this page.

The first question is medical, and it is not ours

Every serious source on this subject starts in the same place, and so must we: house soiling in cats is not first a behaviour question. It is first a question about whether the cat is well. Pain on passing urine, urinary tract disease, joint pain that makes a high sided tray hard to climb into, and conditions that change how much a cat drinks and passes can all present as a cat that has simply stopped using the tray. None of those are things you can rule out from a chair, and none of them are things this site will help you rule out.

So the honest structure of the whole subject is: a vet rules out the medical causes, and only then does the tray itself become the interesting variable. If you skip that order, every environmental change you make is a guess with a sick cat inside it. If you want help getting your side of that phone call in order before you make it, we keep a page on what to have ready and a printable card for writing it down. Neither of them is a diagnosis and neither of them tries to be.

One more thing about drinking and passing urine, because it is where owners most often go looking for a number. We publish a water intake tool and it exists mostly to show how far apart the published formulas are from one another. A change in how much a cat drinks is a reason to phone somebody, not a reason to reach for arithmetic.

What the veterinary profession actually publishes, and who published it

The document to know is Carney and colleagues, AAFP and ISFM Guidelines for Diagnosing and Solving House Soiling Behavior in Cats, published in the Journal of Feline Medicine and Surgery, volume 16, issue 7, pages 579 to 598, dated 25 June 2014. It is a joint guideline of the American Association of Feline Practitioners and the International Society of Feline Medicine, published by SAGE. We read it on 5 August 2026.

It is worth naming the publisher properly, because almost everything you will read about litter trays on a shopping site or a blog is a paraphrase of this guideline with the attribution stripped off. When four different sites tell you the same thing in slightly different words, that is usually not four sources agreeing. It is one source, quoted four times.

The concrete things the guideline sets out, in its own terms:

• A rectangular tray about one and a half times the length of the cat, measured from the nose to the base of the tail.
• Research cited inside the guideline in which adult cats preferred trays measuring roughly 86 by 39 cm.
• A single cat household should have two trays, in separate locations.
• A multi cat household should have at least one tray per cat plus one more.
• Large, open trays are preferred over small covered ones, partly because they let the owner see what is being produced.
• A fine, sand like, unscented clumping substrate, at a depth of at least 3 cm.
• Waste removed at minimum once a day.
• The tray itself washed every one to four weeks, with soap and hot water only.

Reference period matters here and it is rarely given. That guideline is from 2014. Twelve years is a long time in a young field, and a 2014 consensus is a 2014 consensus, not a permanent fact. It is still the most authoritative single document on the subject that we could find, and we are telling you its age rather than letting it read as timeless.

The covered tray question, and the one properly controlled trial

The hood on a litter tray is the argument that will not die. There is, unusually for this subject, a real experiment.

Grigg, Pick and Nibblett, Litter box preference in domestic cats: covered versus uncovered, Journal of Feline Medicine and Surgery, volume 15, issue 4, pages 280 to 284, 2013. Twenty seven cats, one of which was excluded for not cooperating, each given exclusive access to two identical trays for fourteen days. The trays differed in one respect only: one had a hood and one did not. Waste was collected and weighed daily, so use was measured rather than reported.

The result was a flat nothing. Across the group there was no significant difference between the two styles (t equal to 0.44 on 376 degrees of freedom, P equal to 0.66). Broken down by individual cat: 19 of 27, about 70 per cent, showed no preference at all; 4 cats, about 15 per cent, preferred the covered tray; and 4 cats, about 15 per cent, preferred the uncovered one. The authors concluded that where trays are kept sufficiently clean, meaning cleaned at least once daily, most cats will not show a preference either way, and they recommended offering an individual cat a choice rather than assuming.

That is a genuinely useful finding and it is routinely oversold. The American Veterinary Society of Animal Behavior published a piece on 8 December 2024 setting out exactly why. In that trial the trays were considerably larger than the ones sold in shops; the cats were separated from any housemates for the duration; and every tray was scooped daily throughout. Those three conditions are almost never true in a real house at the same time. The honest reading is narrow and it is this: under near ideal conditions, most cats do not care about the hood. It is not the same claim as a covered tray being fine in your home, and the difference between those two sentences is the whole reason this page exists.

Tray size, and a citation we are handing on rather than vouching for

Guy, Hopson and Vanderstichel, Litterbox size preference in domestic cats, Journal of Veterinary Behavior, 2014, is the paper everybody cites for the claim that cats prefer a bigger tray. We tried to read it at source on 5 August 2026 and could not: the publisher refuses automated access to the full text, and the repository copy returned an error. So we are doing the thing that most sites do not do, and telling you that we are reporting this one second hand, as summarised by the American Veterinary Society of Animal Behavior in its December 2024 piece.

This is not a formality. A preference study is only as meaningful as what it compared. Bigger than what? The answer changes the recommendation completely, and we cannot give it to you, so we are not going to write a sentence that implies we can. If you want the reasoning behind why we treat a citation we have not read differently from one we have, it is set out at length on our page on how a published figure is made, which is about poisoning numbers but applies word for word here.

Cleaning, and the direction of the arrow

The AAFP and ISFM guideline asks for waste out at least daily and a wash of the tray itself every one to four weeks with soap and hot water, and that is the recommendation with the most obvious mechanism behind it. Cats bury; a tray they cannot bury in is a tray with a problem.

Padalino and colleagues, 2023, is cited by the AVSAB piece as finding an association between house soiling and infrequent daily scooping. We have again not read that paper at source, and we say so. Even taken at face value it is an association, and the direction of the arrow is genuinely unclear: an owner whose cat has largely stopped using the tray has less to scoop, and may well scoop less often as a result. A study that measures both things at the same moment cannot tell you which one moved first.

The one tray per cat plus one rule, and the study that is missing

This is the most repeated rule in the whole subject. It is printed in the AAFP and ISFM guideline, which is a peer reviewed document from two professional bodies, so it is not folklore. But we went looking for the trial underneath it, and this is what we found.

We could not find a controlled study that varied only the number of trays in a household and measured what happened to soiling. Not one that was hidden, not one behind a paywall we could see the abstract of, none. The nearest thing in the literature is Ellis and colleagues, 2017, in Applied Animal Behaviour Science, which asked a much narrower question about whether a tray that has already been used by another cat is less appealing in a multi cat home. We could not obtain that full text either; the publisher blocks automated access. So we cannot even tell you properly what it found.

Being clear about what that does and does not mean. It does not mean the rule is wrong. It is a sensible rule with a plausible mechanism and the backing of the two bodies most qualified to have an opinion. What it means is that it is a professional consensus recommendation, not a measured result, and those are different kinds of claim. Anybody who tells you the rule is proven should be asked, politely, for the citation. We asked ourselves and we could not produce one.

We take the same line elsewhere on this site when the evidence runs out. On one of our cost pages and on another, the absence of a study is written into the page rather than papered over, because a reader who is told what is not known can weigh what is.

Substrate, location and the things nobody has tested properly

The guideline is specific about substrate: fine, sand like, unscented, clumping, at least 3 cm deep. Three of those four are about texture under the paw, and the fourth, unscented, is about a preference that belongs to the human. Scent in litter is sold to the person carrying the bag, not to the animal standing in it.

Location is where the published record thins out fastest. The guideline asks for trays in separate places rather than lined up in a row, which makes sense if the point of having several is to give a cat a route that avoids another cat. Beyond that, the specific claims you will read, that a tray must not be near the food, that it must not be in a corridor a dog uses, that it must not be beside a noisy appliance, are all plausible and, as far as we can establish, none of them has been tested on its own. They are inferences from what cats are, not results.

If you want to read your own cat rather than a study, the most useful page we have is the one on body language, which is about what a posture can and cannot tell you. Related behaviour pages that owners often arrive at from here: scratching furniture, night calling, biting during handling and sleeping a great deal. None of them will diagnose a tray problem, and all of them are about the same underlying job of watching an animal accurately.

Which of these has a study behind it

Tick anything you have already changed, or are about to. Each one opens to say what class of evidence sits underneath it. Nothing is sent anywhere, nothing is scored, and the panel is plain CSS with no JavaScript in it at all. It will not tell you what is wrong with your cat, because it cannot.

What we could not source

Five things a reader of this page might reasonably expect us to know, and does not get, because we could not find a publisher standing behind them.

1. A controlled trial of tray number. The one per cat plus one rule is printed in a peer reviewed guideline and we could not find the experiment underneath it.
2. The full text of Guy, Hopson and Vanderstichel, 2014. The publisher refuses automated access and the repository copy returned an error on 5 August 2026. We report its result as AVSAB reports it and no further.
3. The full text of Ellis and colleagues, 2017. Same problem. We can name the question it asked and not its answer.
4. The full text of Padalino and colleagues, 2023. Same again, and the direction of its association is exactly the thing we would want the methods for.
5. Any measured figure for how often house soiling turns out to be medical rather than behavioural. Every serious source insists the medical question comes first. We could not find a published proportion, from any country, in any reference period, that would let us tell you how often it turns out to matter. If such a figure exists we would rather print it than this paragraph.

There is a sixth absence worth naming separately, because it is the one that would change this page most. Every study above measures the cat. None of them measures the household: how many people, how much traffic past the tray, whether a dog uses the same corridor, whether the tray is on the floor the cat sleeps on. Those are the variables an owner can actually move, and they are the ones nobody has isolated.

Sources on this page were read at source on 5 August 2026 except where we have said in terms that we were reporting a paper second hand. Where a figure appears it carries its publisher and the year that publisher printed it.

What to do with all of this

Nothing on this page is a plan. If your cat has stopped using its tray, the plan is a vet, and this page exists to make that appointment more useful rather than to postpone it. Take with you what changed and when, whether the cat is straining, what is being produced and where, and whether anything else in the house changed in the same fortnight. Our page on getting your side of the call ready covers that, and this one covers what happens if the answer turns out to be urgent.

If the cat is new to you, the tray is one of the first things to get right rather than one of the last, and our first thirty days page is written around that. If you are budgeting rather than troubleshooting, the annual cost page is the honest version, and it says what it does not know.

Where to go next

• The household litter tray page, for what to change rather than who published what.
• Before you call the vet, and the printable call card.
• Finding an emergency vet, and what happens when you get there.
• The triage helper, which ends in a phone call rather than a score.
• Reading body language, and sleeping a great deal.
• Scratching furniture, night calling, biting during handling.
• If your cat has eaten something, and pet proofing the house.
• How a published figure is made, which is the method behind this page.
• A new kitten, the first thirty days.
• All guides and all tools.

Not veterinary advice. This page describes published research and the gaps in it. It does not diagnose, does not treat, and does not tell you what is wrong with your cat. Only a vet who can examine the animal can do that. If your cat is straining, crying in the tray, producing nothing, or is a male cat failing to pass urine, treat it as an emergency and phone a vet now.