Dog Behavior Problems: Aggression Diagnosis and Overview

Aggression can be a normal part of a dog’s behavior. Dogs use aggressive displays to communicate safely without resorting to physical confrontations. Common low-level signals include direct stares or growls, while more intense signals involve snarls or snaps. These signals communicate messages like "stay back" or "give me space" (see handout "Canine Communication – Interpreting Dog Language").

Aggressive behavior can escalate into a physical confrontation for several reasons. The recipient of the signal could be highly motivated to continue, despite the warning. If the recipient is another dog and responds with its own aggressive signal, a fight could occur if neither dog yields.

Aggressive behavior directed toward people may escalate for a different reason. When dogs use very subtle body language to communicate with people, the signals may not be noticed or understood. When a low level signal is disregarded, a dog can become frustrated. They may then use stronger, clearer signals, such as a snap or bite. A dog may learn to skip low level signals if they continually experience failed communication. Instead of snarling or growling, they may immediately signal a more effective snap or bite. A bite could even seem to occur with little or no provocation, "out of the blue".

"If your dog exhibits a sudden, intense aggressive response, immediately find safety. "

In rare cases, there may be no prior history of aggressive signals or posturing. Dogs can suffer from behavioral illnesses that cause sudden bursts of aggressive behavior. From the start, the aggression may be uninhibited. A dog may inflict a single deep bite or bite multiple times in response to a trigger. If your dog exhibits a sudden, intense, aggressive response, immediately find safety. You may need to walk out of the area, or bribe your dog to go into a quiet room to calm down. If you have been injured, the first step is to take care of yourself. The next step would be to contact your veterinarian to schedule an examination of your dog.

Regardless of the aggression level, you should have your dog examined by your veterinarian. Underlying medical conditions can contribute to aggression. Consult with a qualified behavior professional to have your dog assessed. A veterinary behaviorist or applied animal behaviorist can diagnose, provide a prognosis, and create a behavioral treatment plan to help you prevent unintended reinforcement.

Most of the time, aggressive behavior cannot be fully cured. Depending on the type of aggression, there may be a need for long-term management guidelines to ensure that people and other pets can be safe. If you are concerned for your safety while waiting for a behavioral assessment, discuss medical boarding with your veterinarian.

Will punishment stop my dog’s aggression?

No, punishment will not stop your dog's aggression - quite the opposite. It is not appropriate to punish your dog if you notice an aggressive signal (see handout "Why Punishment Should be Avoided"). Punishment can trigger fear and cause a dog to escalate suddenly. A growl can quickly become a bite. Equally important, when you punish any low level aggressive signal, you effectively teach your dog to avoid low level signals altogether. Unless you have properly addressed your dog’s reason for displaying aggression in the first place, your dog will become frustrated or even anxious as his goals have not been met - his communication attempt failed. Furthermore, if the punishment effectively taught your dog not to snarl or growl, your dog will use a stronger signal such as a snap or bite.

What are some common types of aggression?

To better understand and treat aggression in our companion dogs, it is helpful to consider common underlying motivations for aggressive responses. It is also helpful to consider the context in which your dog behaves aggressively as well as the targets of the aggression. Any dog can have more than one diagnosis, and aggression may be exhibited for more than one reason - which is why a professional assessment is so important. Often, an initial treatment plan requires some triage, focusing on the most urgent, serious, or unavoidable aggressive responses.

Categories of aggression include the following:

Fear based, frustration related, conflict-related, possessive or resource related, food related, protective, territorial, maternal, inappropriate play, redirected, medically or pain-induced, intraspecific (inter-dog) aggression toward familiar and/or unfamiliar dogs, aggression toward unfamiliar people, dominance-related aggression, learned aggression, predatory aggression, and idiopathic aggression. In many cases, more than one form of aggression may be exhibited (see handout "Behavior Counseling: Aggression - Introduction").

Some assessment guidelines for the most common types of aggression are included below.

Fear-based aggression refers to aggression that is exhibited when a dog is frightened. Fearful body postures, in conjunction with aggressive displays, are diagnostic of fear-related aggression. A fearful dog may snarl, growl, or bark as he cowers or moves away from the triggering person or animal. Over repeated exposures, dogs learn that their aggressive response changes the outcome of the encounter. Even though the underlying motivation of fear is unaltered, they appear more confident and, instead of backing away, they begin to rush forward despite their fear.

Another reason for a fearful dog to rush forward can be that, since targets of a threat may retreat for their own safety, the behavior of growling and barking is reinforced and will be repeated (see learned aggression below). Finally, if the fearful dog is punished while trying to retreat, his fear will increase, further motivating him to rush forward in an attempt to make the threat go away. This progression over time can make the assessment challenging and is one important reason to address fear early.

Fear-based aggression can often be successfully treated using a combination of behavior modification, environmental modification, and in some cases, drugs (see handouts "Fears, Phobias, and Anxiety in Cats and Dogs", "Behavior Counseling: Aggression - Introduction", "Fears and Phobias in Dogs: Animals and People", "Fear of Noises in Dogs", and "Fear of Places in Dogs").

Conflict-related aggression refers to aggression exhibited when dogs experience emotional conflict during a social interaction. Generally, the interaction involves either a household person or a person with whom the dog has some social relationship. Dogs in a state of emotional conflict may exhibit a mixture of body postures. They may lean back with one paw up; one ear may be back and one forward; they may snap and then roll onto their side.

Emotional conflict can arise from frustration and/or anxiety related to an interaction. Conflict within a relationship occurs when partners do not behave as expected, or when communication is not clear. Dogs that are sometimes scolded for engaging in a behavior, and other times permitted to do the behavior, may be at risk of developing conflict-related aggression.

One common context in which conflict-related aggression is exhibited is when a dog is approached while they are relaxing. When you approach a resting dog, the dog will often pull their ears back, or stiffen slightly, or roll onto their back. Perhaps the dog is concerned that she will lose her resting place, particularly if she has been evicted from a comfortable spot in the past. She could also be anticipating that she is about to receive medication. She may therefore experience mixed emotions, or conflict, about the pending interaction.

On one hand, if her relationship with the person is good, having her treasured family member join her should be pleasurable. On the other hand, there may be anxiety about being displaced or medicated. There are many possibilities that a skilled behaviorist will help you explore. In any case, the signals are clear: leaning away/ears back/stiff posture reflect emotional discomfort.

"When communication repeatedly breaks down, dogs become frustrated, anticipating emotional conflict."

The dog sending this message would expect the recipient to respond by either stopping their approach or by using a signal to confirm that they do not have any ulterior motive. Healthy communication always flows back and forth until both parties are comfortable. When communication repeatedly breaks down, dogs become frustrated, anticipating emotional conflict. Aggression then progresses from very subtle signals to snarls, growls, and even snaps or bites.

Similar conflict can occur when dogs are approached while they are in possession of something valuable, or even when they are reprimanded. Dogs behave as though they are torn between using an appeasement posture (see handout "Canine Communication – Interpreting Dog Language") or an assertive posture, and aggression with mixed body language is what you see.

Dominance-related aggression refers to aggression that occurs within or during the establishment of a social relationship. Dominance-related aggression is usually motivated by an attempt to control or maintain access to a resource or position. It is a very uncommon diagnosis, particularly in the context of human-dog relationships. Unlike conflict-related aggression, a dog that exhibits dominance-related aggression typically maintains a calm demeanor with no indication of frustration or anxiety. Body language is consistently assertive and aggression is typically inhibited and limited to postural threats. The intensity of aggression can increase when there are repeated conflicts or if the recipient of the communication responds aggressively.

Play-related aggression refers to aggressive behavior that occurs during play. Dogs may become overly aroused during play, perhaps due to frustration, fear, or pain, and suddenly bite hard. They quickly shift away from soft bouncy play posturing to more stiff posture. The dog does not appear to be having fun. Panting or dilated pupils may be evident. It may be difficult to calm or redirect the dog, even after you stop playing. If the behavior is exhibited toward another dog, there could be a physical fight.

In many situations, dogs that play roughly are not exhibiting aggression but are simply playing inappropriately. Injuries can still occur as overly enthusiastic play can include hard mouthing, nipping, and tearing clothing. Dogs that are playing inappropriately appear to be having fun and can often be easily redirected to another activity (see handouts "Dog Behavior Problems – Aggression Between Household Dogs Part 1: Assessment", "Dog Behavior Problems – Aggression Between Household Dogs Part 2: Treatment", "Play Biting in Puppies", and "Dog Behavior and Training: Play and Exercise").

Possessive aggression is aggression that occurs when a dog is in possession of something that is highly desirable, such as a stolen item or a valuable toy. The valuable resource may even be a favored resting place or a special person. The term food-related aggression is often used to describe aggression specifically related to being approached when near food, though technically, food is a resource, and it would be correct to call the behavior resource-related aggression. Food-related aggression may have a genetic component. Dogs that have not had adequate food intake may also be at risk, such as a dog that was abandoned or a dog with medical conditions that increase appetite or affect the dog's ability to process food. Finally, puppies that have had their dishes repeatedly removed while they were eating and dogs that are frequently disturbed while eating may be at risk of developing food-related aggression.

Territorial aggression refers to aggression exhibited when a person or animal approaches the dog’s property. Territorial aggression is most often directed toward strangers and, though pure territorial aggression is mainly related to a combination of reinforcement (learning) and frustration, many dogs exhibiting territorial aggression also demonstrate fear-related aggression toward strangers (see handouts "Puppy Behavior and Training – Socialization and Fear Prevention", "Puppy Behavior and Training – Training Basics").

Territorial behavior, reflected by barking at intruders, is commonly exhibited by most dogs as they mature. Even well-socialized dogs may bark when they notice people or dogs passing by their home or when strangers enter the home. However, with territorial behavior, as opposed to territorial aggression, dogs become friendly once introduced.

Barking is self-rewarding and, in some cases, dogs that have had repeated opportunities to bark can progress to developing territorial aggression. Aggression can occur for several reasons. First, even friendly dogs can become frustrated that the passerby does not visit them. Frustrated dogs increase the intensity of their bark and can eventually become too aroused to relax even when introduced.

Similarly, punishment can contribute to frustration. It may be tempting to reprimand your dog for barking at a passerby or at a visitor that has entered the house. Aversive techniques, whether they are verbal reprimands or physical corrections, are likely to increase the dog’s arousal and frustration. Furthermore, when punishment occurs just as the guests arrive, dogs may experience fear and then associate their fearful emotion with the stranger. Dogs that are fearful, whether through genetics, inadequate socialization, or past experiences (including being punished), are at risk of developing territorial aggression. For treatment of dogs with territorial aggression, see handout "Aggression in Dogs: Territorial".

Protective aggression is aggression directed toward a person or animal that approaches a dog’s special person or companion animal. Dogs exhibiting protective aggression are generally calm, not fearful. They place themselves in front of the person they are protecting and use aggressive displays, ranging from stares and growls to barks or lunges and bites, to prevent the threatening entity from moving forward.

Predatory behavior is the instinctive drive to chase and hunt prey and is not considered to be a form of aggression. The predation sequence includes watching, stalking, chasing, attacking, and most often, ingestion of the prey. Dogs are not emotionally aroused while hunting. When dogs exhibit predatory behavior, they do not typically bark or exhibit any piloerection (hairs standing on end). Some dogs have a strong genetic drive to perform predatory behaviors. Some dogs that have never shown chase or predation on their own may display predatory behavior when running together with a group of dogs. Children may be targeted whether they are running or not.

Predatory behavior is dangerous and cannot be reliably cured. Small pets, including cats, as well as infants, may be targeted. Though there are behavioral training strategies that can help reduce and control predatory behavior, strict management will always be needed. Predators act quickly and silently and their goal is to kill; there may not be enough warning to intervene if they attack.

Predatory aggression is a term sometimes used to describe dogs that excitedly chase and then bite. Most of these dogs enthusiastically chase toys that are tossed, and are described as having a high "prey drive". Aggressive behavior can develop when dogs chase people, most often children, that run away. Joggers, dogs that are running away, and even moving vehicles are often targeted. Dogs often bark as they are chasing, and once they catch up with the target, they are aroused enough to bite. Unlike predatory behavior, dogs exhibiting predatory aggression may respond to treatment, though some management is still needed to prevent injury to young children and small animals. See handouts "Introduction to Desensitization and Counterconditioning", "Dog Behavior Problems: Aggression - Getting Started - Safety and Management", "Dog Behavior Problems: Chase Behaviors", and "Head Halter Training for Dogs".

Maternal aggression is directed toward people or other animals that approach a female dog's puppies. Female dogs that experience a pseudopregnancy (false pregnancy) may become aggressive and begin to protect nesting areas or stuffed toys at the approximate time when the puppies would have been born. The behavior usually resolves once the puppies have been weaned. In many cases, behavioral treatment can be successful and the dog can learn to accept having its puppies handled.

Redirected aggression occurs when the actual target for the aggression is not accessible to the dog. Instead, the dog directs the aggression toward a nearby person or pet. Dogs exhibiting territorial aggression may be at risk of developing redirected aggression, as the target for the behavior is most often something seen outside a door or window.

Redirected aggression includes a substantial component of frustration: dogs that are very aroused jump onto or even bite the recipient. Companion dogs that join an aroused dog and begin to bark are at risk, as are people that attempt to physically move the dog.

Redirected aggression is treated by addressing the dog’s reaction to the trigger. Do not try to physically move your dog while he is barking aggressively. Stand a safe distance away and try to redirect using a favorite toy or treat.

Learned aggression is a component to many forms of aggression, as dogs are always learning. Once a dog learns that an aggressive display is successful at removing the stimulus or changing the outcome of a situation, the behavior is further reinforced and more likely to occur in a similar circumstance in the future.

Dogs that are threatened or punished for aggressive displays may become even more aggressive in future similar situations as they learn to associate the punishment with the presence of the stimulus rather than with their behavior (see handout "Introduction to Desensitization and Counterconditioning").

What are some of the other causes of aggression?

Aggression can be related to underlying medical conditions or medication. Aggression associated with medical disorders may arise at any age and may have a relatively sudden onset. Some diseases and some medications may contribute to irritability. Infectious agents such as rabies, hormonal imbalances such as hypothyroidism, psychomotor epilepsy, neoplasia, and a variety of genetic and metabolic disorders can cause or predispose a dog to aggressive behavior. Painful conditions such as dental disease or arthritis, and medical conditions causing fever, fatigue or sensory loss might also trigger aggression (see handouts "Behavior Counseling: Diagnosing a Behavior Problem - Is It Medical or Behavioral?", and "Behavior Counseling - Senior Pet Behavior Problems").

Idiopathic aggression is used to describe aggression with no identifiable cause and no specific stimuli that initiate the aggressive displays. Idiopathic aggression should only be diagnosed after there has been sufficient diagnostic testing to confirm that there is no underlying disease. It is not yet possible to fully explore the potential chemical and electrical changes in the brain that could contribute to aggressive behaviors. Behavior therapy can be difficult if there are no clear triggers and treatment may include management to assure safety as well as medication to attempt to address possible chemical and electrical abnormalities within the brain.