Aggression is a natural, biological behavior for many dogs. In the wild, dogs hunt and kill prey, fight other dogs to maintain dominance in the pack, and defend their territory. After thousands of years of domestication, most of these instincts have been bred out of household dogs, but a combination of genetic and environmental conditions can bring out the worst aspects of a dog’s behavior and make him a danger to humans. Some degree of aggression can be normal, depending on the specific breed or gender. Dogs often growl or react cautiously to strangers or other dogs they don’t know well, but this is normally limited to harmless posturing. In dogs with behavior problems, aggressive reactions are excessive and dangerous. Dogs may not respond to their owners and will bite and attack without much provocation. Defense of possessions and territory are the most common triggers for negative behavior. Possessive aggression is an extreme reaction to a person or another dog who wants to take or use something the dog sees as his. Territorial aggression can be seen in dogs that attack strangers, such as the mailman, for no reason. In the worst cases, territorial or possessive aggression may be directed toward owners and the dog may become dangerous to live with. In a few cases, a medical condition can be the source of sudden aggression. Hormone changes or pain can significantly alter a dog’s behavior. However most behavior problems develop gradually and are the result of psychological rather than physical problems. Many factors, including genetic temperament, poor training, and negative life experiences, can be related.

Medical conditions, environmental factors, and poor training can lead to aggressive behavior in dogs. Possessive and territorial aggression are the most common types. Dogs will act aggressively in defense of their toys and food, or toward strangers approaching the house or yard.

These are some of the behaviors you might notice in an aggressive dog. Dogs can quickly become dangerous, especially to small children, so discuss the issue with a veterinarian as soon as possible.

These are the two types of aggression most commonly seen in household dogs.

These are some of the reasons a dog might develop aggressive behavior.

Dogs can exhibit sudden behavior changes because of a medical condition, so a veterinarian will need to examine your dog thoroughly and check for signs of illness or pain that could be causing or contributing to the problem. Bloodwork and urinalysis will be needed to see is there if something physical amiss.

Other assessments will be made based on the on your dog’s normal behavior and life history. Training as a puppy, previous owners, and life experiences all play a big part in learned behavior responses, so the veterinarian will want to know about all these areas. Your dog’s family history is also important since some breeds have a higher natural level of aggression. Dogs that are not spayed or castrated also tend to be more aggressive. If your dog’s level of aggression is beyond what is normal for his breed, age, or gender, he will be diagnosed with a behavior problem.

If a medical condition is found to be causing your dog’s behavior problem, the veterinarian will prescribe treatment or pain relievers to help minimize condition. Medication may be needed to balance abnormal hormone levels. Spaying or castrating intact dogs is another way to help reduce aggression. Sex hormones and mating behaviors can exacerbate a natural tendency toward possessive or territorial aggression.

Other treatments will depend on the severity of the problem. For mild behavior problems, the veterinarian may recommend training modifications at home. Obedience training with positive reinforcement can help dogs learn new behavior skills. Non-essential items that are causing aggression can be removed. Keeping the dog confined or on a leash where he cannot see visitors can help to reduce instances of territorial aggression.

For possessive or territorial aggression that is very serious, the veterinarian may recommend working with an animal behavior specialist. Desensitization and counter-conditioning may be necessary to redirect your dog’s negative behaviors. This can be important treatment since dogs that become excessively aggressive are dangerous and may eventually need to be euthanized.

Many dogs are responsive to re-training and make significant improvement, however, it can often take several months for the treatment to have an effect. You may need to take steps to manage the problem in the meantime. Keep the dog away from small children, and try to avoid situations that trigger behaviors as much as possible.

Some dogs will make a complete recovery; others may only reduce the number of aggressive instances. The best way to ensure recovery is to practice the training program put in place by the veterinarian or behavior specialist regularly and consistently. Complete recovery will depend on your dog’s natural temperament, and how ingrained the negative behaviors are.