Sudden Aggressive Behavior in Dogs

Sudden Aggression Could Be a Health Concern

dog barking at stranger
Photo © Jim Corwin/Getty Images

By the time your dog is an adult, you can generally rely on his personality and temperament to stay about the same. So, it can be a shocking to see your easy-going companion suddenly become irritable, begin snapping at everybody, or even act downright vicious. What is a concerned dog owner to do?

Causes of Sudden Aggression in Dogs

It's not normal when a normally happy, loving dog is suddenly aggressive for no apparent reason.

Pain, fear, and illness can all cause sudden behavior changes and temperament changes like aggression. There are many health problems that can affect your dog's personality, some of which can be serious. This is especially true as your dog becomes a senior and begins to develop age-related diseases.

What To Do If Your Dog Suddenly Acts Aggressive

If your dog suddenly acts like he woke up on the wrong side of the bed, you first need to check him out completely and try to determine the cause of his behavior.

  • Check for an external cause. Did something scare your dog? If the aggression was temporary, it might be that your dog was reacting to a perceived threat. However, it's still important to figure out why your dog reacted with aggression if he has not done so in the past. 
  • Locate the source of irritation. Try to find out if he's annoyed by loud noises (possible ear or head trouble), if eating makes him grumpy (mouth or teeth problem), or if he gets snappy when you get too close to him (physical pain).
  • If your dog seems to be in pain, start with a gentle physical exam. Look for swelling, cuts, torn paw pads, insect stings, tender spots; anything that is out of the ordinary.
  • Check the inside of your dog's mouth. It might be a daunting prospect if he's feeling snappy, but the problem could be something as simple as a piece of food, toy or twig caught in his teeth. However, if your dog is threatening to remove your fingers, you should leave this up to a veterinarian.
  • Take note of any and all other possible symptoms (vomiting, diarrhea, loss of appetite, lethargy, etc.). Ideally, write this information down so you can share it with your veterinarian.

Whether or not you are able to determine the cause of your dog's sudden aggression, it is still important that you bring him to the veterinarian. If he's undergone a personality change, then it is serious, and you need to find out what's wrong. Your vet will start by ruling out injuries and other major medical problems. In some cases, sudden aggression can be related to canine cognitive dysfunction. If no medical issue can be found, you may need to seek the assistance of a canine behaviorist

Edited by Jenna Stregowski, RVT