Dog aggression is a frightening experience, and very dangerous for both dogs and people because it can happen as if out of the blue. A very friendly dog can suddenly act aggressively, growling, snapping, and lunging at other dogs and people. At its worst, dogs may attack and cause injury or even death to other dogs and people, including their owners.

In many cases of dog aggression, owners do not know why it happened. Dog owners are usually unaware of the signs of aggression until it is too late. Knowing the potential causes of aggression can help owners see the signs and deal with the aggression before it escalates. Preventing this type of dangerous behavior is far better than dealing with the consequences.

Dog aggression may be due to the following reasons.

Illness or Injury

Pain is a common cause of aggression in dogs. It is not surprising, as people in pain frequently become irritable and aggressive as well. If your dog suddenly shows signs of aggression, it may be due to pain caused by some type of disease, illness, or injury.

Check your dog carefully for injuries. If your dog appears unusually sluggish, quiet, or inactive, starts limping, or stops moving completely, the dog may be sick or have internal injuries. If you cannot figure out the problem, bring your dog immediately to your veterinarian. Do not give your dog any kind of medication, such as pain relievers, unless prescribed by your veterinarian. Giving medication without knowing what is wrong could cause more harm than good.


A dog constantly in fear can become aggressive. Like most animals, dogs may go through freeze, flight, or fight mode when confronted by a dangerous situation.

When dogs sense danger, they will try to escape and get away. If escape is not an option, fear sets in and they will either freeze or fight. In most cases dogs will confront the situation by becoming aggressive, like a rat caught in a trap. It will resort to physical violence to escape the cause of its fear or the source of perceived danger.

Physically abused dogs almost certainly become aggressive because of this fight response to fear. This is very common with rescue dogs many of which are victims of abuse. If you have a rescue dog or if you are not aware of your dog’s history before you got them and they act aggressive, this is most likely due to fear from past abuse.

The best way to get around this situation is to reassure the dog that there is nothing to fear. Be gentle and patient with them. If they show signs of aggression in certain situations, stop immediately and remove them from the environment. Introduce them back to the same situation slowly and with care. It may also be best to consult with a dog trainer that specializes in abused dogs.


Territorial behavior is instinctive for some dogs. Also known as resource guarding, this happens when dogs become very possessive of certain objects or areas of their environment such as food, toys, sleeping area, or their owner. When a person goes near a dog that is eating, playing with a toy, or resting on its bed and the dog displays aggression, it is probably due to this territorial instinct.

The best way to avoid this situation is to respect the dog’s space when engaging in these activities. Punishing or scolding the dog for this will only confuse it. The dog may even take it as a challenge and make the aggression worse. It will not always be easy to understand exactly what the dog is feeling territorial about, but over time it will become apparent.


There are some cases when we need to confine dogs temporarily for safety reasons. Confinement may take the form of a traveling cage, a harness, leash, or a fenced area. Dogs not used to confinement may feel anxious or frustrated when in these situations, and these feelings may manifest as aggression. On the other hand, this may also likely occur when the dog is always in a confined situation, as its frustration from the lack of freedom can build up.

In the former case, it is important to reassure your dog about the temporariness of the confinement. You could do a couple of test runs before the day so they know what to expect. In the latter case, the best way to mitigate aggressive behavior is not to confine your dogs as much as possible. Let them have enough room to run around and burn off excess energy. They are more likely to behave better during confinement if they know they can have some freedom on a regular basis.


The best way to deal with aggressive behavior in your dog is to find out the cause for it. If you are at a loss, you need to consult with a veterinarian or a dog behavior professional. Misinterpreting the cause of your dog’s aggression may lead you to take action that could just make things worse for you, your dog, and those around you.