Sudden Aggression In Dogs: What Could Be The Cause?

You come to depend on your dog. You can generally predict what makes them happy, sad, or tired. You know how your dog behaves around children, cats, and strangers. So, you might feel at a loss when your dog suddenly starts to show signs of unexplained aggression. What has happened to your docile, happy pet?

Sudden behavior changes in  your dog does not usually mean that your pet is finally showing his or her true colors. Instead, there's usually an underlying problem that is causing your dog to show aggression as a means of communicating. Here are some of the causes of aggression in otherwise happy and well-adjusted dogs.


The main cause of sudden aggression in a dog is pain. Your dog may have pain somewhere in the body that causes them to fear anything that might make the pain worse. Your dog might retreat from children who can be rough, or lay the ears back and show teeth to warn them away. If you normally like to scratch behind your dog's ears and they snarl at you, it's a sign that something is wrong.

You might notice your dog is favoring a particular side or resting more often. Sometimes pain can be caused by an illness, like a growing tumor. Whatever the cause, you want to take your animal to the vet to rule out pain issues. 


You probably already know your dog's fears. Some dogs, for example, may fear cats, much to the amusement of their owners. However, new fears can bring out levels of aggression in dogs, especially if they are a completely new or unforeseen situations.

For instance, a dog who is getting older may lose their hearing. Without the familiar sounds of the world around them, a dog can become frightened and uncomfortable, causing him to feel like he must always be on his guard. His level of aggression goes up. Loss of other senses, especially sight, can also trigger aggression in some dogs.

In these cases, restoring senses is not always possible, but you can retrain your dog to adapt to a world that is different than it was before. Instead of using voice commands, for example, you might teach visual commands and keep your dog on a leash near you to help them learn to follow without sound. This can reinforce the bond between dog and master and restore the balance of the pack, which brings a dog security. 


Some illnesses might not cause only pain. There are some types of infections and viruses that can alter neurological systems, including your dog's personality. These diseases, like canine distemper, brain cancer, or rabies, are often fatal, especially by the time behavior changes manifest.

It's still important to consult your vet when you suspect your dog is fatally ill. A diagnosis can help keep other exposed dogs and humans safe; they can be treated for rabies, for example, if symptoms have not yet started to appear. Sometimes, like in the case of distemper, it's kinder to put a dog down than to allow the disease to run its course. Distemper is also contagious to other dogs, and it has no known cure. 

Behavioral Problems

After you've ruled out the medical issues, it's time to look at behavior. Some dogs who have always been well-behaved might feel threatened by a new environment. Examine your life closely for changes. Have you moved to a new house? Did you get another pet? Have you had a baby? Dogs are sensitive to changes in the "pack," and even the kindest dogs can show another side when they are not fully comfortable with the changes. With training and patience, these behavior issues can sometimes be overcome. 

For more information, contact a veterinarian in your area.