10 min.

What your cat's behaviour might be saying about its health

Several causes may explain a suddent change in behavior of your cat. Medical causes are common and it is very important to identify them quickly when they occur.

1. Bigger or smaller appetite

Eating disorders are relatively common in cats. They may be signs of an underlying illness. 

Different types of appetite changes exist; the most common ones in cats are bulimia and hyporexia (or anorexia).


This is a continuous feeling of great hunger, generally leading to the consumption of a large quantity of food. Your cat may be constantly asking/looking for food, and may even try to steal some. The cat doesn't let up until it gets the meal it was after. 

There are various causes of bulimia, including emotional disorders, bulimic rituals (some cats will eat each time they feel happy, such as after being petted), and “classic overeating” (due to boredom or excessive generosity by the owner). But illnesses are also a potential cause (nervous disorders, such as a substitute for anxiety); an increase in your pet's appetite is therefore a reason to consult your veterinarian. 

Hyporexia (or anorexia)

This is the reduction (or total loss) of appetite and the feeling of hunger, leading to lower (or no) food consumption.

The first step should always be to consult a veterinarian if food intake decreases: This is often the sign of a serious illness or great suffering. Additionally, unlike dogs, cats have trouble living with anorexia. It is therefore very important to find the underlying illness as soon as possible. 

2. A cat that hides

Being a hide-and-seek champion isn't really the behaviour of a healthy cat. A cat that suddenly and routinely starts being out of sight is a cat that needs someone to keep an eye on it! 

Many owners unfortunately think it's normal for a cat to start hiding in dark, quiet corners. However, for an ordinary, normally sociable cat, beginning to hide is generally a sign of illness, anxiety, or pain. It's sometimes the only clinical sign that your pet will express, so pay attention to what it's trying to tell you and make an appointment to see your vet. 

3. Difficulty urinating/defecating in the litterbox

When a cat tries but fails to do its business in the litterbox, most people immediately jump to the conclusion that the pet is having a bit of constipation – that it's uncomfortable and bothersome – but nothing much to worry about. Don't make this mistake! 

xIn reality, when a cat seems to be having trouble of this kind, it's generally having trouble urinating (not defecating)! Note that there is no way to tell apart the signs of failed urination and defecation; they are very similar. And besides, although constipation is still worrying, the absolute emergency is urinary tract blockage. 

If you see your cat trying but failing to go in the litterbox, if it vocalizes (meowing, whining) when it tries to use the litterbox, if you see it try to use the litterbox more often than usual, if you see traces of blood in its urine, etc.

Don't wait, contact your vet right away!

If it's a urinary blockage, emergency care is often the only chance for your cat to survive. Even if the diagnosis turns out to be “constipation', don't regret rushing to get it checked out, since it wasn't for nothing; a consultation is still useful in such cases. 

4. House soiling

When a cat suddenly becomes “messy”, it's not uncommon to hear its owners say “it's taking revenge because we came home late” or “behaviour hasn't changed despite severe punishment”. In short, it's not uncommon to hear misconceptions! 

When we talk about house soiling, we mean urinating or defecating outside the litterbox, which the owner finds unacceptable. However, understand that your cat isn't doing it to bug you! More than half the time, this is due to a medical issue. Imagine how doubly painful it must be for a suffering pet, which thinks that the pain it feels when going to the bathroom has something to do with the litterbox, to try to solve its problem any way it can by looking for “less painful” places to urinate and... get punished regularly without understand what's happening to it. 

In short, house soiling must be seen as a red flag to visit your veterinarian. If you and your vet can rule out a possible medical cause, you can explore whether it's a behavioural issue. In any event, the solution will never be to punish your cat. Doing so could become a source of anxiety and make the initial problem worse.

Note: A special article on house soiling is available here.

5. Aggressiveness

Aggression is a behaviour that can be considered “normal” for a cat. It moves from threats to intimidation to fighting. This is a three-phase behaviour sequence: The warning phase, which is meant to intimidate, the consummatory phase (biting, clawing), and the appetitive phase.

It must be understood, however, that aggression is considered a “behavioural disorder” when this sequence intensifies or breaks down (e.g. the pet attacks without first issuing a warning). It is essential to determine the cause of the problem as soon as possible in order to adopt the right solution and decondition the cat away from aggression whenever possible. 

A cat does not become aggressive just “because it's in a bad mood”! First, with your vet, you need to explore: 

  • potential sources of anxiety (cohabitation anxiety, enclosed space/unstimulating space anxiety, etc.)
  • initial causes that may lead to aggression out of irritation and frustration, e.g.: a painful condition (e.g. arthritis) or an aggression due to hunger (often when the food distribution method is ill-suited).

6. Polyuria-polydipsia: My cat is drinking a lot – and peeing a lot

My cat is drinking and peeing a lot; could that mean something? When a cat drinks and urinates more than normal, this is called “polyuria-polydipsia syndrome” (PUPD). And yes, it's a potential sign of a pathological condition; several illnesses may be responsible for PUPD in cats. Consulting a veterinarian is necessary to establish a diagnosis and set up an appropriate course of treatment.

Owners often don't see their cats drink; they will only be worried when the amount of urine in the litterbox increases (or appears more frequently, meaning the litter must be changed more often). If you have a way to measure how much your cat is drinking, do so. Note that your cat is drinking too much if it exceeds 100 mL of water/kg/day. 

The solution is not to ration your pet's water (which would lead to dehydration; if it drinks too much, it's because it feels the need to), but rather to consult your veterinarian as soon as possible. Many illnesses may be responsible for PUPD (diabetes, chronic kidney disease, hyperthyroidism, etc.), and the earlier that care is provided for these diseases, the better.

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.