What to Do If Your Dog Suddenly Becomes Aggressive

Sudden Aggression Could Be a Health Concern

dog barking at stranger
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Has your friendly dog suddenly started showing aggression for no apparent reason? What could cause this sudden change in temperament?

If you have had your adult dog for a while, you can usually predict his response to various situations. In general, you can rely on his personality and temperament to stay about the same. That's why it can be a shock to see your easy-going companion suddenly become irritable, begin snapping at people, or even act downright vicious. The key to dealing with this behavior change is to first determine the cause.

Causes of Sudden Aggression in Dogs

It's not normal when a happy, loving dog suddenly becomes aggressive for no obvious reason. If you take a closer look, you may be able to figure out the cause of the behavior change. 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 quite serious. This is especially common 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 what prompts the behavior. If he's annoyed by loud noises, it's possible he has ear or head trouble. If eating makes him grumpy, it may be a mouth or dental problem. If he gets snappy when you get too close to him, he may be experiencing 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 discuss your dog's medical and behavioral history and perform a  complete physical examination. The goal is to first rule out injuries and other major medical problems. Blood and urine tests may be necessary to assess your dog's cell counts and organ function. Radiographs (x-rays) may also be needed to locate the source of the problem.

In some cases, sudden aggression can be related to canine cognitive dysfunction (dementia), especially if your dog is older. 

If no medical issue can be found, you may need to seek the assistance of a canine behaviorist. An animal behavior professional can help you work with your dog using behavior modification, condition, desensitization, and training.