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Ask a Vet: Why Do Cats Pee Outside the Litter Box?

Last Updated on November 22, 2023 by Catster Editorial Team

Cats certainly are soft, cuddly, loveable creatures. They provide joy and companionship for millions of people. They make wonderful family pets, and cat ownership offers many psychological and health benefits for people.

Sadly, there there is nothing that can destroy the relationship between a cat and its owner more rapidly and thoroughly than house soiling — peeing outside the litter box and on things such as carpets, beds, and other furniture.

I have been a veterinarian for more 14 years. I have been writing about cats on the Internet for nearly a decade. During my career I have interacted with tens of thousands of cat owners online and in person. A very significant number of them have had the same question — a question that I have been asked countless times on Catster and in practice. It boils down to this:

“Why do cats pee outside of the box?”

I understand the question. Cat urine is very special, and not in a good way. Its odor is unique, and house soiling can destroy a home — and the bond between cat and owner — in very short order.

I have written about house soiling before, and I have several pages on my website dedicated to the urinary foibles of cats (here, here, here, and here for starters). But the subject is ever poignant, and information about it is always in demand. I therefore am always on the lookout for the most up-to-date recommendations on the subject.

Enter the American Association of Feline Practitioners and the International Society of Feline Medicine. The two groups recently released the 2014 AAFP and ISFM Guidelines for Diagnosing and Solving House-Soiling Behavior in Cats. From the overview of the guidelines:

The AAFP/ISFM Guidelines for Diagnosing and Solving House-Soiling Behavior in Cats contain scientifically documented information when available and provide practical insight that reflects the accumulated clinical experiences of the authors. The document emphasizes that this unwanted behavior is not due to spite or anger toward the owner, but because the cat’s physical, social, or medical needs are not being met.

The guidelines themselves, predictably because they were created by not one but two major academically inclined organizations, are 21 pages long and replete with political correctness. (Here’s a quote: “The guidelines replace the term ‘inappropriate urination’ with the term ‘house soiling’ because ‘house soiling’ implies no misconduct by the cat.”) What follows is a summary of the guidelines.

The authors report four main causes of feline house soiling. The first consists of medical problems such as bladder infections, bladder stones, urinary incontinence, bladder tumors, and conditions that cause increased thirst and urine production. Furthermore, any sick cat may begin to soil the house even if the primary problem is not related to the urinary tract.

maine coon inside litter box
Image Credit: Nils Jacobi, Shutterstock

Feline idiopathic cystitis, or FIC (formerly known as FLUTD and FUS) is the second cause. Although many consider it to be a medical problem, it is sufficiently common and serious to warrant its own category.

Marking behavior is another common cause of cats peeing outside the box. The final cause is listed as “elimination related to primary environmental or social factors” such as “overcrowding, social competition, and adverse human interventions.” Adverse human interventions are those that cause cats to develop an aversion to the litter box — examples include placing the box near noisy appliances, medicating cats in the box, or ambushing cats while they are using the box.

The authors go on to describe ways to address the problem of cats peeing where they shouldn’t. Vets should manage medical problems if applicable, not assuming that house soiling is a behavioral problem; diagnostic tests should be run on cats that exhibit the behavior.

Once a behavioral cause for the behavior (or behavioral contribution to the behavior) has been identified, the authors recommend two steps: litter box optimization, and fulfillment of the five pillars of a healthy feline environment.

Litter box optimization involves use of the appropriate number (the rule of thumb is that the number of litter boxes should equal the number of cats plus one) and types of boxes. They should be placed in appropriate locations away from food and water. Litter boxes should not be placed close to each other, and they should be distributed in such a way that cats feel safe and are unlikely to suffer ambushes from other cats or people while using them. Bigger boxes are generally better than small ones. Some cats prefer covered boxes, and others prefer open ones. Cats prefer clean boxes. Cats vary in their preferences for different types of litter.

When you think about it, much about litter box optimization is common sense. If the only bathroom available to me were small, filthy, not private, and prone to having strangers kick open the door, I would dread using it. The goal is to make the litter box experience pleasant for cats.

I must confess that I had not previously heard of the five pillars of a healthy feline environment. Upon investigation, it turns out that they were released by (surprise!) the AAFP and ISFM in 2013. After reading them, I agree that they make sense.

The five pillars are:

  • Provide a safe place.
  • Provide multiple and separated key environmental resources (such as food, water, bedding, litter boxes, and scratching areas).
  • Provide opportunity for normal play and predation behaviors.
  • Provide positive and consistent human-feline interactions.
  • Respect the importance of a cat’s sense of smell.

The authors emphasize that house soiling is uncommon for healthy cats that have their social, environmental, and emotional needs met. Meeting those needs is the first step in eliminating house soiling.

You can read the AAFP/ISFM guidelines here.

My recommendations for management of feline house soiling, which are largely compatible with those of the AAFP and ISFM but are substantially more succinct, can be read here.

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About the Author

Dr. Eric Barchas
Dr. Eric Barchas

Dr. Eric Barchas is a professional traveler who spends his spare time working as a full-time veterinarian; contributing to Dogster and Catster; walking, cooking, camping, and exploring the outdoors; skiing (when conditions permit); and reading Booker-shortlisted novels. In between trips Dr. Barchas lives and works in the San Francisco Bay Area with his wife, Denise, and his canine pal, Buster. His main veterinary interests are emergency and critical care, wellness, pain management and promotion of the human-animal bond. Dr. Barchas has to Dogster and Catster since May 2005. 

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