How to Solve Sudden Aggressive Behavior in a Dog

Sudden Aggression Could Be a Health Concern

dog barking at stranger
Photo © Jim Corwin/Getty Images

If you have had your adult dog for a while, you can usually predict its response to various situations. In general, you can rely on your dog's 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 objects or even act downright vicious.

If your dog has suddenly become aggressive, it can be off-putting and scary. The key to dealing with this behavior change is to first try to determine the cause. At the same time, it's important to keep your dog (and human friends and family) safe, by handling the dog in smart, non-aggressive ways, and managing the aggression until you can understand it and then hopefully solve it.

Why Dogs Suddenly Become Aggressive

Aggression is defined as the threat of harm to another individual involving snarling, growling, snapping, biting, barking or lunging. Dogs can also have "leash aggression" which only occurs when on walks and can be include lunging, pulling, and barking, mostly at other 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.

How to Stop Sudden Aggression

If your dog suddenly acts completely different and is quite aggressive, you first need to check the dog out completely and try to determine the cause of its behavior. Walk through this list to help you (and your dog).

  • 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. It's still important to figure out why your dog reacted with aggression if it has not done so in the past. You don't want to be caught off guard or put your dog in a situation that could lead to aggression again.
  • Locate the source of irritation. Try to find out what prompts the behavior. If the dog is suddenly annoyed by loud noises, it's possible it has ear or head trouble. If eating makes the dog grumpy, it may be a mouth or dental problem. If your dog gets snappy when you get too close to it, they 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, or tender spots. Anything that is out of the ordinary could be stressing your dog and causing aggression.
  • Check the inside of your dog's mouth. It might be a daunting prospect if the dog is feeling snappy, but the problem could be something as simple as a piece of food, toy, or twig caught in your dog's teeth. 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.

Next Steps

Whether or not you are able to determine the cause of your dog's sudden aggression, it is still important that you bring the dog to the veterinarian. If the dog has 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.

If the aggression is accompanied by other symptoms like hair loss, weight gain, or lethargy, it could be a sign of hypothyroidism. If aggression is accompanied by convulsion or rapid mood changes, it could be from seizures. Brain damage to specific areas of the brain from diseases like hydrocephalus, tumors, thyroid issues or trauma can also result in aggression problems.

While you are working through the aggression issues with your dog, it's best to limit exposure to strangers, other dogs, or young children. A no visitor rule and no petting rule is best. Also, don't leave your dog unattended and keep them on a leash at all times while you are on walks, in a park, or anywhere else. It's not worth risking a dog bite or potential scare from your dog while you determine where the sudden aggression is coming from.