Understanding and dealing with dog aggression

hen we hear about dog aggression, we all have in memory a story about a relative or friend getting bitten or a traumatic personal encounter with an aggressive dog. In most people's minds, there are good dogs and bad dogs. But the reality is far more nuanced. Dog aggression is a controversial topic, often misunderstood and misdiagnosed.

The number one behavioral problem that motivates dog owners to seek the help of a professional is aggression. Unfortunately, most pet dog trainers and veterinarians are poorly qualified and have limited experience to deal with the problem effectively.

Dog aggression may involve biting, or may just involve threats through aggressive posturing, barking, and growling. Aggression can be directed at humans or at other animals and can take many different forms. It is influenced by genes, sex, age, hormonal status, territory, history, dominance hierarchy, or it can be the result of a learned response. 

Dog bites, in numbers 

According to the American Pet Products Association, there are currently an estimated 90 million dogs in the U.S. kept by 63 million households. The Center For Disease Control (CDC) reports approximately 4.5 million dog bites each year.

  • 80% of dog bites cause only minor injuries that do not require medical attention
  • 70% of bites happen to children under the age of ten
  • Over 50% of the bites occur on the dog owner's property
  • The vast majority of biting dogs (77%) belong to the victim's family or a friend

The CDC reported 38 dog bite fatalities in the U.S in 2018. To put this number into perspective, approximately 1 in 4 million dogs ever kill anyone, and the rate of deaths from dog bites is 8 per million. Which means that you are 1,000 times more likely to get killed in a car accident, and 350 times as likely to get killed by firearms as to be killed by a dog. 

Are dog bites correlated with breed?

Over 30 breeds were associated with dog bite fatalities in the U.S.  The CDC admits that data collection related to bites by breed is fraught with potential sources of error. In recent studies, workers at shelters misidentified dog breeds 50 to 87 percent of the time.

Pit Bulls terriers are reported to be responsible for almost 70% of bite fatalities. But most people don't know that Pit Bulls terriers are four distinct breeds, and even people who are familiar with Pit Bulls have trouble identifying them. Looking closely at the bite fatality data, several common denominators were observed. 55% of the lethal dogs were owned by males in their early 20s who had criminal records, and more than half of the offending dogs showed evidence of physical abuse.

Most organizations, from the Humane Society to the CDC and the ASPCA, oppose breed-specific legislation because of the evidence that it does not help to prevent bite casualties. After banning Pit Bulls in 1984 and euthanizing thousands of animals, Denver has more people hospitalized for dog bites than anywhere else in Colorado.

Chihuahuas are often the worst bite offenders - Dog Learner
Chihuahuas are statistically the worst bite offenders

Types of dog aggression

Animal behaviorists usually regroup the various types of dog aggression into 6 distinct categories. Dominance, possessive, fear, defensive, learned, and idiopathic aggression.

Dominance aggression

There is a very common and unfortunate form of misunderstanding on the subject of pack dominance in dogs that divides dog trainers and owners into opposite camps.

Dogs, like all social animals, have a natural predisposition to find a place in the hierarchy of their social group. But contrary to a simplistic popular belief, dominance does not always imply aggression. In the wild, dogs within a social group can show dominance, but rarely hurt each other. Even among wolves—who are true pack animals and have considerable differences in social structures and behaviors with domesticated dogs—behaviors that are considered as “dominant” or “submissive” serve to maintain unity and coherence within the social group, and is not a sign of scramble for power.

True dominance aggression is rare and often wrongly diagnosed. It has roots in the genes and the social maturity of a dog. Other forms of aggression may have a dominance component, but they are mostly learned behaviors. While working with hundreds of working lines Belgian Malinois and German shepherds training to become police dogs, I have encountered very few dogs that displayed true dominance aggression.

Dominance aggression can simply be provoked by disturbing a dog, approaching his food, his "favorite person", favorite place, or favorite toy. It can be triggered by physical touch (having a collar put on, or grooming). Verbal or physical discipline can provoke or worsen dominance aggression.

According to Victoria Voith, a Professor of Animal Behavior at Western University College of Veterinary Medicine, true dominance aggression is usually seen in male dogs around two years of age, which is the age when dogs socially mature. In 85% of cases, it occurs in males, but it's not puberty related. Castration has little effect on dominance aggression itself, but studies have shown a 60% likelihood that it can significantly reduce inter-male aggression.

Dogs are social opportunists. More dominant dogs can perceive if their owners are weak. When dogs interpret our behavior as a reaction to theirs, they can become more assertive. If you try to win a dog's affection by responding to his demands you can unintentionally reinforce a feeling of dominance in the dog's mind. This is a frequent cause of aggressive behavior in small breeds such as Shih Tzus, Lhasa Apsos, Chihuahuas, or Terriers.

With the help of behavior modification trainers can sometimes alter the mindset of a truly dominant dog, but since dominance aggression is primarily genetic, the problem can never be completely eliminated.

True dominance aggression is rare and primarily genetic - Dog Learner
True dominance aggression is rare and primarily genetic

Possessive aggression

This type of resource guarding aggression is derived from a competitive dominance problem. It occurs more frequently than true dominance aggression, and it is often exacerbated or unintentionally reinforced by human intervention.

This form of aggression can be directed at humans (frequently children), but it's more typically a competitive behavior occurring between dogs similar in size, sex, and age. It can be observed between siblings in pups as young as 6 weeks-old, irrespective of the breed.

Possessive aggression can be associated with food, objects, a sleeping place, or human attention. Jealousy, food aggression, possessiveness over a toy, rivalry over who sleeps in the favorite spot, are all manifestations of learned dominance behaviors where social rules, boundaries and leadership have not been properly established by the owners.

Competitive aggression is less common in breeds that have evolved as pack hounds such as Beagles, and it is more common in terriers that have been bred to hunt singly.

Possessive aggression is best prevented by selecting breeds carefully, and more importantly, training dogs when they are young by establishing clear boundaries and rules. Behavior modification is effective for treating the problem, but old habits die hard and training can get more challenging as dogs get older.

Food aggression must be prevented by training _ Dog Learner
Food aggression must be rehabilitated by training

‍Fear aggression

Of the different types of dog aggression, fear aggression is the one that is the most commonly reported by veterinarians and shelter workers. It can have a genetic component, but it is more typically the result of a previous trauma or a side-effect of stress. It can be a temporary behavior or become a chronic problem that becomes part of the dog's mindset.

Although many types of fear-induced aggression have their origins during the early socialization period of a puppy from 7 to 12 weeks of age, a dog can develop fearful behaviors at any age.

Fear aggression is a defense mechanism. Aggression is often the only way a dog learned to deal with his fear. The fearful dog snaps at someone who approaches, the person backs off, and the dog learns that snapping works (it works with the postman too). The good news is that because it's a learned behavior, it's more treatable than other forms of aggression. 

Fear aggression is one of the most common causes of dog bites of children because fearful dogs are usually touch aversive. Bite statistics show that boys are bitten twice as often as girls, and five to fourteen-year-olds are bitten the most. Dogs that were not socialized to children can be easily spooked by unpredictable or nervous behaviors.

The body language of a fearful dog can be a confusing mix of submissive and aggressive postures. The ears are pulled back, the tail is held low or between the legs and will usually wag in short jerky movements. The lips may be retracted in a snarl, with a show of teeth. The dog's back might be arched and his head held low. He might even display licking movements with his tongue, a submissive gesture that shows fear and nervousness.

A typical body posture of fear in a dog - Dog Learner
A typical body posture of fear in a dog

Behavior modification to treat severe fear aggression usually requires boarding the dog in a specialized rehabilitation program over 2 or 3 weeks, where socialization is gradually associated with desensitization techniques. Most dogs can be rehabilitated successfully.

Although fear-induced aggression has its origins in early learning, there is also a strong genetic component in certain breeds and individuals. Inherited fear aggression is a more difficult problem to fix when it occurs in large breeds such as German shepherds, Dobermans, or Rottweilers.

Defensive or protective aggression

Dogs have an atavistic urge to protect. Protective aggression, or guarding of the home or the family, is viewed as one of the strongest values of canine companionship, but we cannot always predict when dogs will be prompted to be protective. Protective aggression can easily become troublesome, and can be potentially dangerous if a dog is untrained.

In my experience as a behaviorist, this is the second most common form of aggression for which owners seek rehabilitation for their dog, after fear aggression. Unfortunately, many owners of large breed dogs that display this form of aggression do not look for help because they think the behavior is part of the breed's nature and cannot be changed.

The best way to prevent protective aggression is to train the dog in obedience once he reaches puberty. Adult dogs with protective aggression problems can also be rehabilitated successfully, but it can take longer than for younger dogs and generally involves training the owner as well as the dog.

Selective breeding has made guarding or herding breeds genetically predisposed to display protective behaviors, but they are not the only breeds subject to this form of aggression. For example, terriers and Akitas are also known for their defensive instincts.

Generally, the intensity of the territorial or protective drive is genetically inherited and amplified by learning. The German shepherd, for example, makes a great guard dog because of a genetic predisposition to protect and a high capacity to learn. 

On many occasions, I have seen guarding or herding breeds with a strong defense drive —such as Rottweilers or German shepherds— acting protectively when walking with their owner, and displaying unprovoked aggression toward strangers or other dogs. This often occurs when the owner lacks leadership skills or confidence. The dog feels tension on the end of the leash, smells the owner's nervousness or fear, and becomes defensive. These dogs are often described as being leash-reactive, but their behavior goes back to normal when walking with someone else than the owner.

Untrained dogs with high defense drive should wear a muzzle for prevention - Dog Learner
Untrained dogs with high defense drive should wear a muzzle for prevention

Defensive aggression usually first shows itself around puberty in males and females, a period between sexual and social maturity that can happen between 7 months and 2 years, depending on the breed. Territorially aggressive dogs are often friendly on neutral ground such as at the veterinary clinic, but are ferociously aggressive on their own turf.

In female dogs, protective aggression can also be motivated by maternal instinct. Maternal aggression lasts only 2 months during the false pregnancy stage in bitches, or up to 4 months when a litter is actually produced. Frequently, maternal protective aggression occurs when there are no pups. Female dogs can become possessive of objects and fiercely defend them, a form of maternal aggression where the object becomes a surrogate pup.

Learned aggression

Dogs can be taught to be aggressive. Some dogs are treated with cruelty to induce aggression. People who train dogs for fights choose them from breeds that were selectively bred for this purpose, such as Bulldogs or Pit Bulls, and use pain to provoke aggression. 

Most forms of dominance and protective aggression can be developed or redirected to our advantage through learning. This is how police dogs are trained in crowd control. In the right hands, learned aggression can be turned on and off. A police dog is trained to be relatively friendly and sociable among the public, yet the dog might at any moment be required to switch to an offensive mode and attack a suspect on command.

Idiopathic Aggression

Dogs that suffer from idiopathic aggression are typically affectionate, obedient, and well-mannered canines who can suddenly turn ferociously on their owners or on visitors. The aggression is not related to dominance, fear, protection, or any other known cause, and in these circumstances, it's called idiopathic aggression, or colloquially "Rage Syndrome".

Several breeds are known to be more genetically predisposed to this rare condition, including English Cocker spaniels and Springer spaniels, Bernese Mountain dogs, Saint Bernards, Lhasa Apsos, Rottweilers, Doberman Pinschers, and German shepherds.

There is no known effective treatment for idiopathic aggression. In most cases veterinarians recommend euthanasia because of the potential threat that the dog poses.

How to prevent dog aggression


Many forms of fear-induced aggression can be avoided through proper socialization of pups. Puppies should be exposed to people, children, other pets, loud noises, and all forms of stimuli between the age of 6 to 12 weeks. A puppy that is gradually flooded with sensory stimulation at an early age is less likely to be fearful when he grows up.

Puppies can be tested before 8 weeks for behavior and temperament. Although testing is not always an accurate predictor of future behavior, studies have shown that pups that test positive for aggressive dominance at 8 weeks tend to remain dominant as they grow older.

Adult dogs

If you adopt a dog from a shelter, you should enquire about the dog’s history. If you have doubts about a dog you wish to adopt, ask a behaviorist to test the dog at the shelter.

Dominance aggression can also be avoided through careful breed selection. Unless you are experienced with handling and training dominant dogs, you should avoid adopting ancient breeds (Akita, Malamute, Basenji, Chow Chow, Shar Pei) or breeds that have a genetic predisposition toward dominance aggression (such as terriers, herding or guarding breeds).

If a dog starts to repeatedly display aggressive behaviors, find a qualified dog behaviorist who can diagnose the nature of the aggression and offer a rehabilitation program.

When considering behavior rehabilitation for aggression, you should take into account the possibility that you may unintentionally exacerbate aggressive behaviors through reinforcement, or lack of leadership. You may need help from a trainer to learn to modify how you interact with your dog.

Dogs who display aggressive behaviors should be preventively fitted with a muzzle until they are rehabilitated. Do not be tempted to use a prong collar or a shock collar on an aggressive dog. These devices should only be used in training by professionals. When used in the wrong manner, or with the wrong dog, they can make aggression worse or make the dog turn against you.

Teach children to respect a dog’s food, space, resting place, and toys.

Dogs with aggressive tendencies should attend obedience training classes as early as possible. At home, you should give your dog clear rules and boundaries. You may see your dog as your best friend but you should not forget that dogs need boundaries and a leader they can respect. If you don't take leadership in a calm and assertive way, your dog will.

Never physically punish an aggressive dog, as it can trigger further aggression.

Identify the exact circumstances under which fear aggression occurs. This is important because in rehabilitation we need to recreate the context that triggers the dog. The best rehabilitation method is to desensitize the dog by gradually exposing him to the fearful stimulation at a lower intensity, and rewarding him for not showing aggression.

Remember that stroking your dog to calm him when he shows signs of fearful aggression reinforces the problem. You are actually encouraging his aggressive behavior by rewarding his fear with touch and attention.

The simplest treatment is to counter-condition the guarding or over-protective dog to be friendly with anyone who comes on to his territory. This is done by withdrawing all rewards or toys from the dog and only rewarding him when visitors arrive.

Dealing with an aggressive dog

  • Don’t approach an unfamiliar dog, and learn to observe and read a dog’s body language to assess if he is displaying dominance or fear.
  • Do not run from a dog, panic, or make loud noises. If an unfamiliar dog approaches you, remain motionless, and avoid direct eye contact.
  • Do not disturb dogs while they’re eating, sleeping, or taking care of their puppies.
  • A fearful aggressive dog is best approached with calm and non-threatening energy. Don’t back off, but stand sideways without making eye contact, touch, or sound. Give the dog a chance to retreat and calm down once he realizes that he's not under threat.
  • If you have a protective or dominant dog, make sure to use the right type of leash and collar. Martingales collars are safe and effective, as dogs cannot back out of their collar and escape your control. With a reactive dog, never use a retractable leash or aversive accessories such as head halters or prong collars.
  • Do not attempt to separate fighting dogs on your own, especially by pulling them away by their collars, as this is a sure way of getting bitten. The way to separate fighting dogs is for two people to grab and lift the hind legs of each dog to pull them apart.
  • A dominant or protective dog should not be antagonized unless you know what you are doing. Don't start a fight that you are not sure to win. Fearful or protective dogs can sometimes bluff aggression to scare people away. When confronted with a more dominant response —such as threatening gestures, waving an object or making loud sounds—many dogs won't attack. However, that's a risky strategy, unless you have nerves of steel and are experienced in controlling aggressive dogs. Be aware that a truly dominant dog will not back off.

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