Reasons Why Dogs Get Aggressive and How to Stop It

Prevent your dog from biting you aggressively

Causes of Aggression in Dogs

The Spruce / Katie Kerpel

Whether it is directed towards you or another family member, a stranger, or another animal, an aggressive dog can not only be very frightening, but may also lead to injury or legal action. But although it may seem like your dog is biting you aggressively or showing other aggressive behaviors out of the blue, most dogs only exhibit aggressive behavior for one of five basic reasons: Your dog is ill, frightened, possessive, showing dominance, or frustrated.

Understanding the reasons why your dog is biting, growling, or showing other aggressive actions is the first step in resolving this potentially dangerous behavior. Too many owners assume that an aggressive dog is out of control and must be rehomed or euthanized. However, once you take steps to resolve the situations causing your dog to act out, you'll often find that the aggression disappears or is greatly reduced.

Here's what you need to know if your dog is getting aggressive with you, family members, pets, or strangers.

Why Do Dogs Show Aggression?

Knowing why your dog is acting aggressively is essential to figuring out the best plan for stopping this frightening behavior. First, however, it helps to know the signs of canine aggression, as few dogs bite without first showing escalating behaviors that indicate an attack is coming. A dog displaying aggression may:

  • Stand very still with a rigid posture
  • Make direct eye contact and hold it
  • Flatten the ears against the head
  • Growl or bark in a threatening tone
  • Snarl
  • Curl its lips to expose its teeth
  • Lunge forward without making contact
  • Snap without making contact
  • Bite lightly so as not to break the skin
  • Bite hard enough to break the skin or leave a mark

Depending on the cause and intensity of the stimulus provoking the aggression, a dog might progress through all of these behaviors, or might just deliver a warning by growling, snarling, showing aggressive body postures, or exposing its teeth without progressing to an actual bite.

Most often, your dog will display aggression due to one of the following five reasons.

Illness and Injury

Some medical conditions can cause dogs to become aggressive. If a dog that has never shown any sign of aggression suddenly begins growling, snapping, or biting, it may be caused by a disease or illness.

Pain is an especially common cause of aggression in dogs. Your suddenly aggressive dog may have an injury or an illness that's causing major discomfort and stress. Some possible causes of pain include arthritis, bone fractures, internal injuries, various tumors, and lacerations.

Other illnesses may affect your dog's brain, leading to seemingly unreasonable aggression. Conditions such as cognitive dysfunction and brain diseases or tumors may provoke the onset of aggression. These problems are more likely to occur in older dogs but can happen at any age.

If your dog is exhibiting sudden, unexplained aggression, talk to your veterinarian before attempting to address it as a behavior problem.

You may be tempted to try giving your dog medication to relieve pain, but this is something you should not do. If your dog is sick, you'll need to know exactly what is wrong with it before you begin any treatment. Don't try to take matters into your own hands until you know what you're dealing with. Only a veterinarian can advise what medications are appropriate for your dog.


A fearful dog can easily develop aggressive behavior. Most dogs only exhibit aggressive behavior if they sense that they are in danger, cannot escape, and feel the need to defend themselves. For example, this may occur if a dog is backed into a corner with no way out, or if it thinks a hand raised over its head means it is going to get hit.

If your dog is a rescue dog that exhibits more aggressive or fearful behavior than is normal, it may have been abused, neglected, experienced a traumatic event, or not properly socialized as a puppy. Any information you can get from the organization where you adopted the dog could help you determine the best way to handle the situation.

Sometimes rescue dogs need obedience training with an instructor who specializes in teaching dogs that have been abused or those that have not been properly socialized. In some cases, you may be able to manage your dog's fear on your own with training and patience. You can speak to a veterinarian about the best course of action.

To avoid provoking this type of aggressive behavior, approach unknown dogs carefully (better yet, let them approach you). Train and socialize your dog to help prevent fear down the road.


Possession aggression, or resource guarding, occurs when a dog is possessive of something. This is often food, toys, or some other object of value. A dog that exhibits possession aggression may growl if someone approaches his food bowl or gets too close when he is chewing a favorite toy.

A dog may also bite or show aggression to a stranger who steps into your home or onto your property, which is the dog's territory. This is a common scenario with dogs who "hate the mail carrier" or bark violently at people just outside the property boundary or fence.

Resource guarding is also a common cause of aggression towards other household pets. Some dogs will growl, snap, or bite other animals in the home who approach the dog's food bowl, bed, or favorite toy.

The degree of aggression may vary from one dog to another and between objects. For instance, your dog might not care if you sit down and pet him while he chews a rubber toy, but he may turn and snap at you when you do the same thing while he chews a pig's ear. It all depends on the value that the dog attributes to each object or resource.

Dog pulling toy from man's hand
gollykim / Getty Images

Show of Dominance

Dogs sometimes behave aggressively as a display of dominance. This is often directed toward other dogs, but it can occur with people as well.

It's important to understand that dominance is a behavior, not a personality trait. Dogs are not dominant or submissive "by nature". Some may have tendencies towards one behavior or the other, but this is typically determined by the circumstances.

Dogs that display dominant behavior feel that they must prove they're in charge of a situation. The growling, snapping, or biting occurs when they feel their position is being challenged.

Unfortunately, people often mistake the cause of canine aggression as dominance-related behavior when there may be another cause. In reality, aggressively dominant behavior is not nearly as common as the other causes of aggression.

Two Dogs Fighting On Lawn

Cindy Biell / Getty Images


Aggression that's caused by frustration is often referred to as redirected aggression or barrier frustration. It occurs when a dog is frustrated at not being able to get to something and takes its frustration out in another way. This type of aggression is common in dogs that spend a lot of time tied up, restrained on a leash, or behind a chain-link fence.

For example, a dog that's chained in a yard may spend the day straining to get to a dog that lives across the street or in an adjacent yard. The restrained dog usually barks and growls more fiercely as the frustration grows. When the owner approaches, the dog may redirect its frustration and bite the owner. Redirected aggression may also result in the dog lashing out at another family pet, whether canine or feline.

Be careful not to misinterpret your dog's aggression. Always rule out a health issue or fear before you assume you know the reason for your dog's aggressive behavior. Otherwise, attempts at corrective measures could actually make the problem worse. If you are unable to get to the root of your dog's aggression, it can help to hire a professional dog trainer that specializes in canine aggression. These specialists have knowledge and training methods that can be very effective even with dogs that seem to be "lost causes."

If you suspect your pet is sick, call your vet immediately. For health-related questions, always consult your veterinarian, as they have examined your pet, know the pet's health history, and can make the best recommendations for your pet.
Article Sources
The Spruce Pets uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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