top of page

Aggression in Dogs

Updated: Sep 4, 2023



Dogs can become aggressive, and a veterinary doctor needs to be consulted to rule out any medical cause. Canine aggression is a stressful, unwanted behaviour for both owners and veterinarians. When an animal encounters social situations that he or she does not like, aggression is utilized to change it. Usually, the animal does this by using threats to indicate potential harm should the encounter continue. There are various types of aggression in dogs hence the importance to determine why a dog is aggressive. Canine aggression is usually complex to treat and can be dangerous.

How is aggression classified?


Aggression is a complicated condition to evaluate and is exhibited differently in each dog. Some dogs may exhibit a single form of aggression, while others may exhibit several types of aggression at the same time. Understanding the different types of aggression can help get to the root of the problem:

Dominance aggression (also called impulse control aggression) occurs when a dog threatens or attacks people for correcting his or her behaviour, e.g. physical restraint and control of food and toys.

Fear-aggression occurs when a dog is afraid and the dogs often urinate or defecate during the episode. The dog becomes aggressive when he or she can no longer avoid a frightening situation but is initially passive or withdrawn.

Inter-dog aggression is usually directed at other dogs inside and/or outside the household.

Maternal aggression occurs when a mother dog is excessively aggressive towards people who she feels are threatening her puppies or towards the puppies themselves.

Pain aggression is a protective reaction by a dog in pain and occurs when a dog is touched or moved or anticipates being handled.

Play aggression occurs with play behaviours such as chasing but vigorous play (eg tug-of-war) by people does not necessarily lead to play aggression in dogs.

Possessive aggression occurs when a dog thinks that a person or animal may try to take a toy or other non-food object.

Predatory aggression is associated with predation (e.g. stalking, hunting, or catching small animals) and usually involves a sudden attack, a severe bite, and shaking of the prey. It is often silent, often resulting in a lightning-quick approach to the prey animal hence very dangerous if directed towards humans. It is often a behaviour the dog or cat enjoys although it is dangerous and lethal for the receiving animal. With dogs, it is often directed towards fast-moving objects but can be directed towards joggers, cyclists, skaters and running, screaming children. This aggression often causes a baking behaviour if the dog cannot get to its prey, e.g., when a dog barks with frustration at a bird or possum in a tree or at a cat beyond a fence.

Protective aggression occurs when a dog guards members of his or her pack or owner against another animal or person who may not pose an actual threat. Whelping dogs are also extremely protective of their puppies and may become hostile toward anyone who goes near them.

Redirected aggression occurs when a dog cannot attack an intended target (e.g. person or animal) and redirects his or her aggression toward another target, e.g., the dog might become aggressive toward a person who attempts to break up a dog fight, or if it happens that the dog can't reach the target of its hostility, e.g., a neighbouring dog on the other side of a fence.

Territorial aggression occurs when a dog protects a place or its space, e.g., a yard or a house, from another animal or a person who may not pose an actual threat but the dog deems as an intruder.

What are the Common Triggers of Aggression in Dogs?


There are several causes of aggression in dogs and here is a list of nine common reasons for aggressive behaviour.

1. Grumpy

Whether human or animal, once in a while they are allowed to be grumpy. This is manifested mostly in dogs where their space has been invaded or a puppy has stretched their patience. Unfortunately, grumpiness tends to manifest as aggression in dogs.

2. Fear

When dogs are afraid, they sometimes act aggressively in preparation for a fight or a flight. The dog could be frightened of loud noises, certain types of people, specific smells or picking up on social and emotional cues and respond aggressively e.g. when you’re angry or fearful.

3. Puppyhood

Traumatic puppyhood, e.g., rescues, can make puppies aggressive later in life. A life of neglect, abuse, or a lack of socialization, can make them act out because that is the way they learned how to regulate their feelings of uncertainty as puppies. Dog behaviour training can help to counter this.

4. Dislike of other Animals

Though dogs are more forgiving than most people, sometimes they just don’t like certain other animals. It could be cats, birds, or other dogs, but sometimes it can be small children or specific demographics of people.

5. Injury or Sickness

When a dog acts out aggressively with little warning, there is a high chance that he is sick or injured. Though external injuries are easily visible, an injury that is hidden or sickness can cause aggression that seems unexplainable. Illnesses like tumours, internal bleeding, arthritis, bone fractures, cognitive dysfunction, ear infections, and toothaches are things that can cause aggression that is unexplainable.

6. Anxiety

Abrupt changes in the home can cause dogs to feel anxious, and cause them to act out aggressively. Things like a move, a new baby, or a new pet can all cause anxiety that can lead to aggression.

7. Possessive or Territorial

Overly possessive or territorial dogs within the home or when on a walk on a leash, can become a safety issue. Dogs need to learn how to share items and spaces so that everyone can have a fun time.

8. Frustration

When overly frustrated, dogs – like humans – often act aggressively. For dogs, frustration-aggression is usually manifested when chained up for long periods of time or being in a compound with a chain-link fence. When they see so many fun things to do, the frustration of not being able to do them can result in aggressive behaviour.

9. Dominance

Dogs are pack animals with a highly evolved hierarchy among themselves. “Social aggression” is always manifested when new dogs are met and a new hierarchy needs to be figured out. Since aggression is a behaviour – not a trait – how it is addressed can make it more or less ingrained in their personality.

Signs of aggression


The following are signs of increasingly intense behaviours that may be exhibited in an aggressive dog though not sequentially:

  1. Becoming still and rigid

  2. Threatening barking

  3. Lunging or charging at a target without making contact

  4. Mouthing a person or animal to move or control him or her

  5. "Muzzle punching" - the dog punches with his or her nose

  6. Growling

  7. Showing teeth

  8. Snarling - a combination of growling and showing teeth

  9. Snapping the mouth

  10. Nipping quickly without leaving a mark

  11. Biting quickly and tearing the skin

  12. Biting, resulting in a bruise

  13. Biting, resulting in puncture wounds

  14. Rapid, repeated biting

  15. Biting and shaking

Dogs don't always follow the above sequence, engaging in several of the behaviours simultaneously. Dogs don't become aggressive abruptly and rarely bite without warning. Medical issues can cause some dogs to become aggressive e.g.

  1. any type of pain,

  2. an orthopaedic (bone or joint) problem,

  3. a thyroid gland abnormality,

  4. adrenal gland dysfunction,

  5. cognitive (brain) dysfunction,

  6. a seizure disorder,

  7. loss or decrease of senses such as vision or hearing).

Geriatric dogs that feel confused or insecure may also become aggressive. Besides, certain medications can alter your dog's mood, possibly causing a dog to become aggressive. Certain situations can also upset a dog causing him or her to become aggressive.

Questions that need to be answered to ascertain these situational causes include:-

  1. Who or what was the target of the dog's aggression?

  2. When and where did it happen?

  3. What else was occurring at the time?

  4. What had just happened or was about to happen to the dog?

  5. What seemed to stop the dog's aggression?

Answers to these questions can clarify the circumstances that trigger a dog's aggression and can help the owner and the vet understand the reasons for a dog's behaviour.

How do I know if a dog is being aggressive or just playing?


Though it is difficult to tell the difference between non-aggressive and aggressive nipping and mouthing by dogs, most dogs use their mouths out of fear or frustration, indicating an aggression problem. In most instances, playful dogs have:-

  1. a relaxed body and face.

  2. the dog's muzzle might look wrinkled, but the facial muscles are relaxed.

  3. playful nipping or mouthing is usually not painful.

An aggressive dog often has

  1. a stiff body,

  2. a wrinkled muzzle, and

  3. exposed teeth.

Aggressive bites are usually quicker and more painful than playful nipping or mouthing.

What are the risk factors to consider when considering keeping and treating an aggressive dog?


The following factors need to be considered seriously:

  1. Size: Large dogs inflict more damage than small dogs.

  2. Age: young dogs are easier to treat against aggression than older dogs.

  3. Bite history: dogs with a biting history are a known risk and an insurance liability.

  4. Severity: aggressive dogs that do not bite are safer to have than dogs that bite.

  5. Predictability: dogs that give little or no warning before they bite are high risk. Dogs that warn before they bite give an allowance for people and other animals time to avoid getting hurt.

  6. Targets: the ability to manage and treat a dog's aggression is affected by how often the dog is exposed to his or her targets of aggression, e.g., a dog that is aggressive toward strangers may be easy to control in a rural area with a securely fenced garden. A dog that is aggressive toward children is easier to manage if children are seldom around.

  7. Triggers: the triggers that cause a dog to become aggressive should be avoided, e.g., if a dog is only aggressive while eating, the solution is easy: stay away from the dog while he or she is eating.

  8. Reproductive status: spaying or neutering can help with several forms of aggression.

  9. Motivation: The safest and most effective way to treat aggression is to use behaviour modification under the guidance of a qualified professional. Modifying a dog's behaviour involves motivation by rewards for good behaviour, so success is more likely if the dog enjoys praise, treats, and toys. Dogs that aren't very motivated by these rewards are a challenge to train, so the likelihood of improvement is lower.

How can canine aggression be treated?


A treatment plan should be designed and supervised by a behaviour specialist as treating canine aggression is usually complex and can be dangerous. A veterinary behaviourist or a certified professional dog trainer who has training and experience in treating canine aggression should always be consulted. The dog needs to be assisted to avoid situations that cause him or her to become aggressive, reducing the risk of a dog biting someone. Physical punishment, including the use of prong collars and electric shock collars, is not recommended as it can worsen a dog's aggression or make the dog afraid.



Landsberg G, Hunthausen W & Ackerman, L (1997) Handbook of behaviour problems of the dog and cat. pp 145-146.

Overall K L (1997) Clinical behavioural medicine for small animals. pp 104-105, 113, 131-134, 244-245.

Askew H (1996) Treatment of behaviour problems in dogs and cats. pp 175-176.

Borchett P L & Voith V L (1982) Classification of animal behaviour problems. Vet Clin North Am Sm Anim Pract 12, pp 571-585.

40 views0 comments


bottom of page