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My cat is being aggressive towards my other cat, what should I do?

Aggression is one of the most common problems seen in behavioural practice. Aggression can be defined as a threat, challenge or attack that is directed towards one or more individuals. Aggression may be normal or abnormal depending on the context in which it occurs.

There are many different reasons why cats can be aggressive towards other cats. To be able to successfully treat the problem, it’s essential to work out what the underlying cause, or trigger, is. To do this, we recommend that you consult with a qualified veterinary behaviourist (your local vet can refer you). They will ask you lots of questions and may also visit you in your house so they can observe your cat in their own environment and their interactions with other cats in the household.

Medical conditions can cause aggression so it is important to rule out any underlying medical causes prior to addressing behavioural causes for aggression. Brain disorders, liver disease, epilepsy, poor hearing or sight, pain-inducing disease (e.g. arthritis) and hormone imbalances can cause aggression. Certain medications, including anaesthetic agents and corticosteroids (e.g. cortisone) have also been associated with aggression.

Some of the underlying non-medical causes for aggression between cats in the same household include fear, lack of socialisation, inappropriate introduction of a new cat, overcrowding (i.e. not enough vertical or horizontal space, too few resources etc), redirected aggression, play and predation.Some of the underlying causes for aggression between cats outside the household (neighbourhood cats) include fear, lack of socialisation, introduction of a new cat in the territory, hormonal (entire males or females) and redirected aggression.

Signs of aggression may be visual (e.g. changes in body posture, erect fur), auditory (e.g. growling, hissing), olfactory (e.g. urine spraying) and may involve use of teeth and claws.

This article provides some basic advice about five common types of aggression directed at other cats and how to deal with them:

  1. Fear aggression
  2. Inter-male aggression
  3. Play aggression
  4. Redirected aggression
  5. Territorial aggression

1. Fear aggression

Fear aggression may be exhibited in a combination of offensive and defensive responses. The fearful cat may initially attempt to avoid the fear stimulus if that is an option. Fearful cats will typically hiss, spit, growl, pilo-erect (fur stands up), flatten their ears against the head and show a low or crouched body position. Pupil dilation is common. He/she may try to flee or attack, depending on the circumstances. Aggression is usually the last resort but it is often violent and over time may become learnt. Spraying may also occur.

Underlying causes

Cat personalities can be divided into two main genetic types: timid, fearful cats or confident, friendly cats, and this may account for some fearful behaviours. Inadequate or lack of socialisation prior to 12 weeks of age may also contribute to the cat’s responses. Cats can learn to be fearful of certain situations, especially if they have had an unpleasant experience with no opportunity to escape.


Depending of the severity of the problem the cat may need no treatment or may need behaviour modification, such as desensitisation and counter-conditioning, in combination with medication in severe or long-standing cases. Behaviour modification involves desensitisation and counter-conditioning by slowly introducing the cat to the fearful situation in a gradual, controlled sequence. Firstly, the cat is offered a tasty treat such as vegemite, chicken, or dehydrated liver. Then, while the cat is eating, the fearful stimulus (other cat) is gradually introduced at a distance. The initial distance should be great enough not to cause any fearful response from the cat.This gradual approach may vary from days to months depending on the severity of the problem. The cat should not be forced into the fearful situation as that will exacerbate the fear. Putting several bells on the cat’s collar at varying intervals so that the victim has a warning signal of the other cat’s presence has proved to be helpful.Medication may also be needed (your vet will advise). The synthetic pheromone, Feliway®, can also be beneficial. Punishment, or forced restraint will aggravate the situation and must never be used as it is likely to increase the anxiety and impede learning.

2. Inter-male aggression

In male-male aggression the cat flattens his ears, howls, hisses, pilo-erects and uses both the teeth and claws in fights. The signs may be either active (threatening) or passive (blocking access).

Underlying causes

This type of aggression usually starts in entire males at 2-4 years of age when they reach ‘social’ maturity. In some cases it may be normal male-male aggression associated with mating. It increases during the breeding season and with overcrowding. In neutered cats it tends to appear later and it may be associated with social role (status).


Pre-pubertal and post-pubertal castration reduces or stops the frequency of fights in about 90% of cases between entire males. Treatment may also involve changing the social environment. Cats in the same household should initially be separated so that no visual contact is possible and reintroducing them slowly as described for redirected aggression. It is important not to try to introduce them too fast, or too soon. In some cases permanent separation is necessary. Medication may also be needed (your vet will advise). The synthetic pheromones, Feliway® can also be beneficial.

3. Play Aggression

Cats often stalk, chase, pounce and lay in wait as a from of ‘play’, but this can also involve aggression in the form of biting and scratching. It is sometimes difficult to recognise play aggression as some cats play more roughly than others and do not retract their claws when they swat.

Underlying causes

Targets are usually moving objects or people and may be another cat, especially an older one, in the household. Young cats, especially those that are orphaned, hand raised or weaned early, are more likely to show this type of aggression and in many cases it may be normal behaviour.


The aim of treatment is to redirect the play behaviour onto more suitable objects rather than trying to stop the behaviour completely. One way of achieving this is to provide the cat with appropriate toys, for example cat dancers®, cat wire toys, or cat tracks® (only use toys that are safe for cats – avoid string toys which can become an intestinal obstruction if swallowed) on which to pounce and direct these behaviours. However, the toys need to be changed at regular intervals, even daily, for the cat to maintain interest. The cat may first need to be taught how to play, and then encouraged to play with toys.

Direct punishment, such as smacking, must not be used as this may encourage the behaviour and may lead to other problems, such as fear aggression or redirected aggression. A regular routine that involves interactive play time involving toys 2-3 times daily for 5-10 minutes is important to provide a natural outlet for the behaviour.

Placing several bells on the cat’s collar at varying intervals has been advocated so that the victim has a warning signal of the cat’s presence. Acquiring a second kitten, preferably one that is not very young, may also help to teach the cat more appropriate behaviour.

4. Redirected Aggression

Redirected aggression occurs when the original target of the aggression is not accessible and the cat now directs its aggression towards an unrelated target, a person or another cat, that enters the area soon after.

Underlying causes

The eliciting factors of the aggression are different in the initial and subsequent episodes. The first episode is often missed by the owner and is triggered by a stimulus that the cat is unable to respond to. The cat is now highly aroused and directs its attention onto the next thing she/he sees. For example, a cat sees another cat through a window, but is unable to reach it. Another cat in the household then enters the room and the cat redirects the aggression to the second cat. In the second, and subsequent episodes, the initial stimulus no longer has to be present to elicit the aggression, just the target of the first attack.

Commonly, the behaviour of the target also changes and this then results in a prolonged conflict, with the second cat now acting warily, running away, and showing avoidance behaviour whenever the first cat enters the room or approaches.


The cat should be left alone until it is calm and no attempt should be made to try to calm or reassure it. If another cat is involved, then the cats should initially be separated regardless of whether it is the victim or the instigator of the aggression. Treatment then involves slowly reintroducing the cats to each other, (the same way a new cat is introduced into the household). They should be placed in separate rooms so that they can hear and smell each other, but no visual contact occurs. The cats should be rotated around all the rooms in the house until they have left their scent in every room. While the cats are separated, a regular routine should be established so that certain events such as feeding or playing occur at a set time each day. Ideally the cats are fed 5-6 small meals each day. The aim is for them to have a positive association with each other on re-introduction. This essentially means that ‘good’ things such as play or feeding will only happen in the presence of the other cat.

The cats are then slowly reintroduced. Initially they are only in the same room during meal times. They are placed in cages at opposite ends of the room and are fed at this time. This should create a positive association with food and the presence of the other cat. If no hissing or spitting occurs and the cats eat the food, the cages are gradually brought closer and closer to each other over a period of days and meals. This may take several weeks. Then one cat at a time is allowed out of its cage to explore and, if no aggression occurs, then both are allowed to interact under supervision. The re-introduction needs to be slow.

In some cases medication may also be needed (your vet will advise). Synthetic pheromones – Feliway® diffuser plugged into the room can also be beneficial to decrease anxiety. Your vet will advise.

5. Territorial Aggression

The cat may patrol its territory and mark it by rubbing or spraying to maintain social distance as well as define hierarchy. The cat is aggressive to another cat that approaches or enters his territory and he may attack.

Underlying causes

The behaviour may be more marked in entire toms in the breeding season. Unfamiliar cats are less well tolerated than familiar or neighbouring cats. The aggression decreases with increased distance away from the territory.


An accurate diagnosis is essential if the problem is to be successfully resolved. If the aggression is directed towards another cat within the home they may need to be separated and reintroduced as described above. Putting several bells on the cat’s collar at varying intervals helps so that the victim has warning signal of the cat’s presence.

In some cases, medication may also be needed to treat the cat (your vet will advise). Physical punishment must not be used as it will exacerbate the problem.

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Updated on April 30, 2019
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