Dogs can become aggressive and bark, growl, lunge at, and even attack other pets and people for all kinds of reasons — dominance, fear, defense of territory, pain, frustration, overly enthusiastic play, and more. The safest and most effective way to treat aggression is behavior modification under the guidance of a qualified professional. Drugs may sometimes help, but early socialization is the very best preventive.


Aggression is among the most common behavior issues seen in dogs. It typically includes the kinds of behaviors we associate with threat or attack, such as barking, growling, and biting. In most cases aggression is perfectly appropriate, as when dogs bark to warn other dogs of their territorial limits or growl in response to threatening sounds.

However, some dogs will display increasingly intense versions of this normal behavior. This typically progressive manifestation of aggression in dogs can be dangerous to humans, other dogs, and other animals that may share the same household. In these cases, the aggression may be treated as a disease and, as such, is often cited as a common cause of death in dogs since relinquishment to shelters (and subsequent euthanasia) is a common sequela of the aberrant forms of this behavior.

Severe forms of canine aggression may have a hereditary component, as with the disease colloquially referred to as “rage” that afflicts certain lines of dogs. This form of aggression is considered deeply pathological and rare and, as such, will not be treated here.

It should also be noted that aggression can be appropriate, as well. Though dogs have been domesticated by people for a long time, it is important to remember that they are still animals with a very strong instinct for “fight or flight” when danger is present. When presented with a threat, many dogs will try to escape; however, some dogs will choose to fight against the danger and may bite in response to the threat, which is why it’s important to follow certain safety guidelines when working with dogs to avoid injury.

Signs and Identification

Aggressive dogs usually exhibit some part of the following sequence of progressively more 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” — when 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 dogs bite, so they think that their dogs have suddenly become aggressive for no apparent reason. However, dogs rarely bite without warning.

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 nonfood 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.
  • 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.
  • 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.

Affected Breeds

A dog of any breed can become dangerously aggressive. Though genetic predispositions are known to exist within lines and perhaps even among entire breeds, most versions of canine aggression are considered preventable and treatable. (This issue is highly controversial as it often comprises the basis for breed-specific legislation.)


Behavior modification therapy is the most common method for treating canine aggression. Pharmacologic intervention is also commonly employed by veterinarians and veterinary behaviorists, but never as a standalone modality. Behavior modification is always the cornerstone of treatment.

In any case, 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.

In general, the following issues will determine the severity of the problem and need for lengthier professional treatment timeframes:

  • 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 aggressive only 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.


Prevention of canine aggression is possible. The most critical feature of this approach involves early and frequent socialization with humans, dogs, and other animals. Puppy socialization with people should begin as soon as possible, and socialization with other dogs can begin once your veterinarian has administered the necessary vaccines. The degree to which socialization is critical to the prevention of aggression cannot be overstated.

As to preventing injury: Common steps to avoid injury include using proper restraint. This can vary depending on the dog, but at minimum, a collar or harness and leash in good condition should be used when handling a dog. Consult with your veterinarian about appropriate collars for training. It is vital to have the dog in a secure environment (e.g., a room with a closed door or a fenced yard) and ensure that the dog’s collar is secure, or the dog may be able to escape the collar and run away. In some cases, additional restraint such as a muzzle may be necessary.

Introducing dogs slowly to new situations or new dogs can be helpful to avoid agitating them. However, it is not always possible to avoid new situations, so it’s important to be prepared to teach the dog alternative behaviors and provide positive reinforcement to diffuse the situation.

This article has been reviewed by a Veterinarian.