• If your dog has become aggressive, consult your veterinarian to rule out a medical cause.
  • Understanding the various types of aggression in dogs can help you determine why your dog might be aggressive.
  • Do not use physical punishment on your dog. Hitting your dog could cause him or her to become afraid or more aggressive.
  • Treating canine aggression is usually complex and can be dangerous, so a treatment plan should be designed and supervised by a behavior specialist.

The Basics

The most common and serious behavior problems of dogs are associated with aggression. Canine aggression includes any behavior associated with a threat or attack (e.g., growling, biting). Aggressive dogs usually exhibit some part of the following sequence of increasingly intense behaviors:

  • Becoming still and rigid
  • Threatening barking
  • Lunging or charging at a target without making contact
  • Mouthing a person or animal to move or control him or her
  • “Muzzle punching”—the dog punches with his or her nose
  • Growling
  • Showing teeth
  • Snarling—a combination of growling and showing teeth
  • Snapping the mouth
  • Nipping quickly without leaving a mark
  • Biting quickly and tearing the skin
  • Biting, resulting in a bruise
  • Biting, resulting in puncture wounds
  • Rapid, repeated biting
  • Biting and shaking

Dogs don’t always follow the above sequence, and they often engage in several of the behaviors simultaneously. Owners often don’t recognize the warning signs before a dog bite, so they think that their dog has suddenly become aggressive for no apparent reason. However, dogs rarely bite without warning.

If your dog has become aggressive, it is crucial to take him or her to your veterinarian in order to rule out medical issues before you do anything else. Some dogs are aggressive because of a medical condition (e.g., any type of pain, an orthopedic [bone or joint] problem, a thyroid gland abnormality, adrenal gland dysfunction, cognitive [brain] dysfunction, a seizure disorder, loss or decrease of senses such as vision or hearing). Geriatric dogs that feel confused or insecure may become aggressive. In addition, certain medications can alter your dog’s mood, possibly causing your dog to become aggressive.

If a medical cause of your dog’s aggression has been ruled out by your veterinarian, think about the situations that upset your dog. Who or what was the target of your dog’s aggression? When and where did it happen? What else was occurring at the time? What had just happened or was about to happen to your dog? What seemed to stop your dog’s aggression? Answering these questions can clarify the circumstances that trigger your dog’s aggression and can help you and your veterinarian understand the reasons for your dog’s behavior. Understanding the various types of aggression in dogs can also help you determine why your dog is aggressive.

Types of Aggression

Aggression can be a complicated condition to evaluate. 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 behavior. Situations that provoke this aggression include physical restraint and control of food and toys.
  • Fear aggression occurs when a dog is afraid. Affected dogs often urinate or defecate during the episode. The dog is initially passive or withdrawn but becomes aggressive when he or she can no longer avoid the frightening situation.
  • Interdog aggression is directed at other dogs inside and/or outside the household.
  • Maternal aggression occurs when a mother dog is excessively aggressive toward people who she feels are threatening her puppies or toward the puppies themselves.
  • Pain aggression is a protective reaction by a dog in pain. This aggression can occur when a dog is touched or moved or anticipates being handled.
  • Play aggression occurs with play behaviors such as chasing. Vigorous play (e.g., 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). This aggression usually involves a sudden attack, a severe bite, and shaking of the prey.
  • Protective aggression occurs when a dog guards his or her owner from another person who may not pose an actual threat.
  • Redirectedaggression occurs when a dog cannot attack an intended target (e.g., person or animal) and redirects his or her aggression toward another target.
  • Territorial aggression occurs when a dog protects a place, such as a yard or house, from another animal or a person who may not pose an actual threat.

Play Versus Aggression

It can be difficult to tell the difference between nonaggressive and aggressive nipping and mouthing by dogs. Some dogs use their mouths out of fear or frustration, which can indicate a problem with aggression. In most cases, playful dogs have a relaxed body and face. During play, your dog’s muzzle might look wrinkled, but the facial muscles shouldn’t look tense. Playful nipping or mouthing is usually not painful. However, an aggressive dog often has a stiff body, a wrinkled muzzle, and exposed teeth. Aggressive bites are usually quicker and more painful than playful nipping or mouthing.

Risk Factors

You are ultimately responsible for your dog’s behavior. If you are deciding whether to keep and treat your aggressive dog, consider the following factors:

  • Size: Large dogs are more frightening and can inflict more damage than small dogs.
  • Age: Young dogs that are aggressive are thought to be easier to treat than older dogs.
  • Bite history: Dogs that have already bitten are a known risk and an insurance liability.
  • Severity: Aggressive dogs that do not bite are significantly safer to have than dogs that bite.
  • Predictability: Dogs that give little or no warning before they bite are at the highest risk of being euthanized for aggression. Dogs that warn before they bite allow people and other animals time to avoid getting hurt.
  • Targets: The ability to manage and treat your dog’s aggression can be affected by how often your dog is exposed to his or her targets of aggression. For example, a dog that is aggressive toward strangers may be easy to control if you live in a rural area with a securely fenced yard. A dog that is aggressive toward children can be easier to manage if children are seldom around.
  • Triggers: Are the triggers that cause your dog to become aggressive easy or impossible to avoid? For example, if your dog is only aggressive while eating, the solution is easy: stay away from your dog while he or she is eating.
  • Reproductive status: Spaying or neutering can help with several forms of aggression.
  • Motivation: How easy is it to motivate your dog during training? The safest and most effective way to treat aggression is to use behavior modification under the guidance of a qualified professional. Modifying a dog’s behavior involves rewards for good behavior, so success is more likely if your dog enjoys praise, treats, and toys. Dogs that aren’t very motivated by these rewards can be challenging to train, so the likelihood of improvement is lower.


Treating canine aggression is usually complex and can be dangerous, so a treatment plan should be designed and supervised by a behavior specialist. Look for a certified applied animal behaviorist (CAAB or ACAAB), a veterinary behaviorist (DACVB), or a certified professional dog trainer (CPDT) in your area. If you choose a CPDT, be sure that he or she has training and experience in treating canine aggression.

Helping your dog avoid situations that cause him or her to become aggressive can reduce the risk of your dog biting someone. Physical punishment, including the use of prong collars and electric shock collars, can worsen a dog’s aggression. Therefore, punishment of aggression is not recommended.