10 min.

House soiling: investigate before blaming the cat!

House-soiling problems are unfortunately one of the most common reasons why cats are abandoned. However, if you examine the root cause of this behaviour, it becomes clear that it can often be solved, especially if you ask yourself the right questions in time.

Definition: What is “house soiling”?

This term refers to defecating or urinating on horizontal or vertical surfaces in places that are considered unacceptable by the cat owner (without considering the cause of such behaviour).

Note: We prefer the term “house soiling” rather than the traditional term “inappropriate elimination”. The term “inappropriate elimination” seems ill-suited to us, because from the cat's perspective, this behaviour is not inappropriate, it is just meeting a need as it normally does. Calling it “house-soiling” emphasizes that the place where it is doing its business is unacceptable or undesirable... to the human! This term emphasizes the human being's responsibility to provide the animal with an appropriate environment that the cat will also consider appropriate.


There are many factors that can explain house-soiling problems when the cat is leaving its waste somewhere other than the spot designated by the owner.

Urinary marking (communication)

  • Territory/Protecting resources
  • Status/'hierarchical” position (sexual or social status)
  • Anxiety

Choosing other places to go

  • Behavioural causes: preferences or aversions
  • Medical causes

Although marking is a communication process, going outside the litterbox can have either medical or behavioural causes.

Urinary marking

Urinary marking (spraying urine, territorial or social behavior) must be distinguished from regular urination. This is a normal method for cats to communicate with one another. Marking is most commonly done by unneutered male cats, but this is not a hard-and-fast rule.


Standing, tail vertical and wagging

Soiled surface


Quantity of urine emitted

Low (drops)



Start of sequence

Flehmen (mouth ajar with nose turned up)

End of sequence

No covering

The cat marks whatever is unknown with “adoption marks” and whatever has already been marked with “maintenance marks”. Marking indicates both geography and time: It sets off a portion of space with an olfactory barrier and allows the marking cat to tell time by sensing the gradual decrease in the olfactory signal.

Marking may become pathological, which means that the behaviour does not allow for appropriate adaptation to changes in the environment. Any alteration of the cat's marking behaviour may be a sign that it is developing a behavioural illness or disorder. 

In adult cats, make an appointment with the vet if you see an increase in scent-marking, in order to find any health issues, particularly anxiety disorders. For instance, an increase in spraying may be initiated by a territorial change (move to a new house, furniture being rearranged, change in the owner's routine, arrival of a new family member, etc.). If the stress persists and is generating anxiety, pathological marking may set in. Other signs may accompany these behavioural changes: Aggression, bulimia/anorexia, sleep disorders, motor defects, etc. 

Choosing other places to go

Medical causes

Most of the medical causes that may be behind house soiling affect the urinary tract (idiopathic cystitis, stones, urinary infections, etc.). Other illnesses that lead to an increased urine volume (such as diabetes), diarrhea, or constipation, are also potential causes. Environmental factors may also play a role, often as a source of stress to the pet, as is the case with idiopathic cystitis. 

You should always consult a veterinarian when you first see signs of house soiling, in order to rule out or diagnose such illnesses as soon as possible.

Behavioural causes

Behavioural causes associated with house soiling may, in some cases, stem from the cat's preference for doing its business someplace else: Most of these behavioural causes stem from the cat's aversion for the litterbox (either the litter itself, the tray, or how clean it is kept). 



Soiled surface


Quantity of urine emitted

High (puddles)


No (unless pathological)

Start of sequence

Scratching (unless aversion to litter)

End of sequence

Covering (unless aversion to litter)


Cats' preferences and aversions for litterboxes:

How much a cat enjoys or disdains a litterbox may be measured by various indicators. For instance, cats which dislike their litterbox tend to hesitate near it and avoid entering, or do less to cover their excrement or scratch the sides of the tray or the surrounding surface rather than the litter itself.


Litterbox cleanliness is one of the main causes of litterbox aversion among cats. This is often observed in cats that only have access to a covered box, which keeps nauseating odors stuck inside. Some cats prefer to relieve themselves in better-aerated places. If so, keeping the box cleaner or offering an open one may fix this problem. 

Note that the American Association of Feline Practitioners (AAFP) and the International Society of Feline Medicine (ISFM) recommend daily removal of solid waste from the litterbox. Clumping litter makes this procedure easier.

Ammonia smells

Ammonia, a gas that causes strong smells specific to dirty litterboxes, is produced when the urea contained in urine is broken down by bacterial enzymes. Cats (just like human beings) are repulsed by strong ammonia smells. It is also worth noting that ammonia is toxic and can cause numerous health problems. 

In order to minimize or prevent the production of ammonia from urea, high-quality litters use an ammonia smell remover, which helps cats enjoy the box and reduces the risks of house soiling.

Types of litter

Litter aversions may also be caused by using too much fragrance or too coarse a texture. Cats prefer unscented (or lightly scented) litters made of fine grains, often with clumping qualities. 

The majority of cats also seem to have a clear preference for clay-based litter, as their texture is similar to the soil in which wild cats defecate. 


The location of the litterbox is also a key factor. When the cat has trouble getting to its box, the risk of house soiling is greater. Things which may inhibit box access include a hostile multi-cat environment, the presence of children or noise, or a feline health issue. Cats prefer calm, private, safe, easy-to-get-to places.

Boxes that do not contain enough litter, are too small, or contain linings that claws could get caught in may also lead to aversions.

What we ask of cats

Indoor cats are kept in an environment that is generally more suited to human lives than their own nine lives. We ask them to tolerate our own lifestyle. 

Cats have what is called a “tolerance level” that is different for each one, which defines how far they are prepared to tolerate multiple human adaptations. Above that level, their cooperation is by no means assured, and they may express a “stress behaviour” (which may be marking or choosing other places to relieve themselves, or it may be aggressiveness or scratching, etc.).

In the “tolerance zone”

Little is asked of the cat – Its environment respects its needs, e.g.:

  • Litter is of good quality, well-kept, little or no fragrance
  • Boxes are well-placed
  • Places where the cat can play/hide, etc.
  • Routine with no unpleasant surprises (moving houses, new resident, etc.)

“Stress behaviour”

Much is asked of the cat – Its environment does not do enough to respect its needs, e.g.:

  • Litter is of poor quality, not well-kept, too much fragrance
  • Boxes are poorly placed (e.g. close to food)
  • Unwanted housemates from the cat's perspective (e.g. other pets)
  • Owner's routine keeps changing / Owner is absent for a long time
  • Not enough toys/hiding spaces in the environment

Solutions to house soiling

Step 1: Always consult a veterinarian!

Frist, identify the type of house soiling (marking OR choosing other places to go). The next thing to do is rule out any illness as an underlying cause. 

Illnesses, particularly urinary ones, are often the cause of house soiling. Treating the disease – if there is one – is the first step to ending house-soiling.

When the cat is marking territory

Marking is often due to sexual hormones, so getting your cat fixed is one option that you could discuss with your vet. If the marking is pathological, other problems in your cat's environment should be explored – they might be sources of anxiety. 

When the cat is choosing other places to go

You will need to figure out whether your pet has just found a new place to go to the bathroom that it finds more to its liking (like a flowerpot or rug, etc.) or whether it is averse to what it finds in its current environment.

About the author

Elodie Khenifar
Veterinarian, M.Sc. (Pathology & Microbiology.)
Vet Consulting Medical Director for Intersand and Laboratoires Blücare, Boucherville, Québec, Canada

Dr. Khenifar, a graduate of the Ecole Nationale Vétérinaire de Toulouse [Toulouse National College of Veterinary Medicine] worked in a mixed veterinary practice before completing a Master of Veterinary Science degree (Pathology & Microbiology) at the Université de Montréal Faculty of Veterinary Medicine in Saint-Hyacinthe, Québec. 

Since 2017, she has been the medical director at Intersand and Les Laboratoires Blücare, where she oversees veterinary science communications.