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Aggression In Dogs

When dogs exhibit aggressive behaviors, it is always upsetting.

By gaining a better understanding of aggressive behavior, you can better prevent, manage, and modify aggression in your dog.


Aggression is a category of behaviors, all of which are a response to a perceived threat. These behaviors include:

  • Growling

  • Tooth displays of varying degrees

  • "Muzzle punch" (striking with a closed mouth)

  • Snapping (without contact)

  • Biting without injury

  • Biting with varying degrees of injury

There are many non-aggressive ways dogs attempt to avoid or escape a threatening situation before escalating to aggressive behaviors but too often these early warning signs aren't recognized by most dog owners. The exception to this description is predatory behavior which, although violent, is linked to food acquisition and not aggression.


Aggressive behavior in dogs is most frequently caused by fear and stress due to various factors including, but not limited to:

  • Lack of proper and early socialization

  • Lack of training

  • Unskilled use of aversive methods (bad training) (1)

  • Traumatic experience

  • Genetic predisposition (poor breeding)

Medical issues can also contribute to aggressive behavior. In the last ten years, dogs that came to me with reported aggression were diagnosed (by the dog's veterinarian) with hypothyroidism, Cushing's Disease, mast cell cancer, urinary tract infections, hip and elbow dysplasia and more. This is why a trainer may refer you to your veterinarian for blood work and other testing if illness or injury is suspected.

Some types of aggression may be neurological. There was a popular internet video of a dog protecting his bone from his own foot. This is a very good example of a behavior problem that has medical or neurological causes. These types of behaviors require the assistance of a veterinary behaviorist, as training is not enough.

What are not causes of aggression:

  • "Spoiling" the dog (2)

  • Playing tug games

  • Not being pack leader-y enough

In most cases we see, the main causes of aggressive behavior are lack of or improper early socialization and/or the unskilled use of aversive methods and equipment, either on their own or at the hands of an individual advertising as a professional dog trainer.


There's no shortage of websites claiming that "dominance is the leading cause of aggression." But is that really the case?

The subject of dominance is worthy of it's own article and we recommend AVSAB Position Statement on Dominance pdf for a complete definition and explanation of what it is...and what it is not.

Bottom line: The vast majority of aggression is a response to a perceived threat, not some attempt at total world domination.


No matter what the headlines say, no matter what one person's individual experience has been, breed is never a predictor of aggression.

Golden Retrievers are as capable of aggression towards humans or other dogs, as Pit Bulls are capable of working as therapy dogs and search and rescue dogs. It is the individual dog, not the breed, that must be considered.


Except in very rare cases, aggression is not random. This is why a dog that shows aggression toward strange dogs is not likely to act aggressively towards family members. A dog that displays aggression towards strange people may be perfectly friendly when meeting new dogs. So why does it seem to occur without warning?

Dogs give numerous subtle signals of anxiety or discomfort that aren't recognized by most dog owners. When these signs of stress are ignored, the dog may feel the need to escalate to a signal that is more clear to humans, such as growling, snarling or snapping.

Common signs of stress/anxiety include:

  • Avoidance of people or other dogs

  • Looking away

  • Turning away

  • Pulling away

  • Walking away

  • Repetitive yawning

  • Repetitive licking of the lip/nose

  • Tense body language

  • Slow movement

  • Low tail carriage

  • Backward ear carriage

When owners fail to recognize these signs, they may continue to put the dog in stressful situations. Finally, the dog escalates to a clear sign of discomfort, causing the owners to claim the dog was "fine" previously and that the aggression appeared without warning.

A professional trainer will teach you how to read your dog's body language, so you will be able to recognize when your dog is anxious.


There is no such thing as an "aggressive dog," as no dog will exhibit aggressive behaviors 24 hours per day. Aggression is not a breed characteristic or personality trait. Aggression is always a response to something in the dog's environment, whether it is the action of a human, the sudden appearance of another dog, pain caused by injury or illness, and more. This is called an antecedent, which means a preceding occurrence, cause or event. Antecedents are also called triggers.

In order to determine the triggers for your dog's aggressive behavior, it is necessary to gather a detailed history of each incident. A professional trainer can work with you to determine a pattern in the situations that have triggered your dog's aggression. Once these triggers are identified, a training/behavior plan can be devised.


Dogs make choices in the form and level of aggression they use to communicate with us or with other dogs. If a minor form of communication, such as a small growl, is enough to achieve the goal of stopping a person from taking a bone or another dog from mounting, the dog has no need to escalate to a higher level of aggression.

Even when biting, dogs make decisions as to the location and severity of the bite. The vast majority of bites inflicted by dogs never cause injury. These are still bites, by definition, but the dog has chosen to use a warning without injuring the offending person or dog. Because dogs are so much faster and more accurate than we are, these non-injurious bites are not because the human moved quickly enough to avoid the bite, but that the dog chose not to cause damage.

For information about the levels of dog bites see Dr. Ian Dunbar's Dog Bite Scale, which many trainers use as a guideline.


Aggression is not an illness or something that can be removed, it is an instinctive reaction to a perceived threat. Just as no one can train you not to defend your family if they are threatened by a burglar, you can not train out a dog's instinct to protect itself. All dogs are capable of aggression, regardless of breed.

What behavior modification CAN do is decrease your dog's stress around the situations that used to trigger aggressive responses, teach your dog an alternate behavior she can perform in those situations (such as look at you instead of bark at strangers), and even form positive associations to the situations that were previously a problem. The level of positive association will depend on many different factors. In the case of dog-dog aggression, some dogs may eventually be able to play with new dogs after a careful introduction. For others, they may only learn to tolerate dogs at a distance (such as walks), but never learn to like other dogs.

In order for a behavior modification plan to be successful, a careful management strategy must be implemented. This strategy will be customized to each dog and household and will be designed to prevent aggressive behavior from recurring while you are going through the training process.


Many owners and even some people advertising as trainers believe that the best way to address aggression is to provoke the dog into reacting, then applying some form of punishment to teach the dog that aggression is "wrong."