Why Is My Dog Being Aggressive?

As a pet owner, you likely recognize how important it is to keep your dog from being aggressive. And of course, no one wants to have an overly aggressive dog in the home, either. But what do you do if your dog has suddenly become aggressive when they were not before? What does this mean?

There are many potential underlying causes of a dog becoming suddenly aggressive. Typically, a sudden behavior shift like this indicates something is wrong. Read through the article below to try to narrow down what could be going on with your pet, and don’t hesitate to take them to the veterinarian as soon as possible.

dog aggression

Your Dog Could be in Pain

Pain is the most common cause of sudden aggression in dogs. Pain can cause a dog to become frightened, which may lead to lashing out; on the other hand, dogs may become so defensive and protective of themselves when in pain that they become aggressive.

If you suspect your dog is in pain, take them to the vet or emergency vet to figure out what’s wrong as soon as possible. Your dog may have suffered an acute injury that needs to be treated, or they may have a larger-scale problem that should be resolved.

Fear and Anxiety in Dogs

If your dog’s aggression has started occurring at times when they are upset, afraid, or anxious, then you can probably safely assume the two are related. Dogs who are very frightened may sometimes lash out in aggression, even toward their trusted human family members. On the other hand, dogs who are anxious may become aggressive if they are bothered or feel unsafe for any reason.

Try to determine the underlying cause of your dog’s fear and aggression. From there, you can work on training your dog to recognize when issues are not really threats, or you can try to remove the issue instead.

Chronic Disease

Chronic disease is any type of disease that lasts indefinitely for your dog. If your dog is dealing with chronic illness and pain, they may not feel very well, and this could contribute to the foul mood. A dog who is constantly dealing with illness is more likely to become aggressive for this reason.

Cancer is one type of chronic disease that can contribute to aggression in dogs. Additionally, if your dog has a brain tumor, this disease could cause behavioral changes as well. Arthritis is yet another problem that can cause aggression in normally passive dogs.

Acute Illness

Acute illness could include a wide range of problems. This type of illness could be something as simple as a respiratory infection that is making your dog feel bad, or it could be something much more serious instead.

Keep in mind that sudden aggression is also a symptom of rabies. Although rabies is not very common these days, it is still possible that an unvaccinated dog could have contracted rabies. If you know your dog isn’t vaccinated and has become suddenly aggressive, have them checked for rabies right away. Always keep your dog up to date on vaccinations to prevent this deadly and frightening illness.

Pregnancy Could Cause Aggression in Dogs

If you have a female dog and she has not been spayed, there is always a chance she could be pregnant. Just like humans, dogs go through mood swings when they are pregnant and dealing with changes in their hormones. A pregnant dog may be excessively clingy or could be aggressive and standoffish, depending on her mood.

If your dog is pregnant, you’ll need to talk to your veterinarian about the best way to help her throughout the pregnancy. You should also make sure you are ready to bring puppies into your household and know what you’ll do with the puppies after they come.


Some dogs may become confused about where they are or who they’re with when they get older. This type of canine dementia may lead to frequent bouts of aggression, especially if your dog is surprised or startled.

Unfortunately, there is not a known cure for canine dementia. The best solution when dealing with this problem in your dog is to keep your pet as comfortable and content as possible throughout the rest of their life. Your vet may be able to give you further suggestions that are specific to your dog.

Talk with Your Vet About Dog Aggression

Sudden changes in behavior almost always have an underlying problem that is causing them. If your dog’s behavioral changes have happened over a short amount of time, it’s important to take them to the vet to figure out what’s going on.

Your vet can help you determine whether the problem is truly behavioral, or if it is related to a physical health problem instead. By working with a trusted Heart + Paw vet, you can also choose the best treatment or management solution for your pet moving forward.

If your dog is being aggressive, book an appointment online at any of our Heart + Paw locations to talk with a vet.

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Heart + Paw was founded in 2018 by Chief Veterinary Officer Dr. George Melillo, who currently serves the Mid-Atlantic area. Heart + Paw offers a combination of veterinary care, pet grooming, and dog daycare to help be a resource in your pet parenthood journey.

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