One of the most important steps in dealing with dog aggression is finding out the cause of the aggression. Knowing why your dog is acting aggressively can help you figure out the best plan for stopping the frightening behavior. The following are some of the causes of aggression in dogs:

Illness

There are a number of illnesses that cause dogs to become aggressive. If a dog who has never shown any sign of aggression suddenly begins growling, snapping, or biting, it may be caused by a disease or illness.

Brain tumors, thyroid disease, and rabies are just a few illnesses that may cause the onset of aggression. Talk to your veterinarian to determine whether a disease may be the cause of your dog's aggression.

Establishing Dominance

Dogs often show aggression to establish their dominance. Dogs who display this type of aggression feel that they are in charge. The growling, snapping, or biting occurs when they feel their dominance is being challenged. If your dog is displaying aggression in an attempt to establish dominance, he may snap, growl, or bite when you try to move him off the furniture, restrain him, grab his collar, or give a leash correction.

Fear

Fear is another reason a dog might display aggression. Usually, the dog only exhibits aggressive behavior if he feels he is in danger and needs to defend himself. This can occur if a dog is backed into a corner with no means of escape, or if a dog perceives the hand you raised over his head was to hit him rather than pet him. A fearful dog usually only bites when he feels he is unable to escape some impending harm and must defend himself.

Possession Aggression

Possession aggression occurs when a dog gets possessive of food, a toy, a bed, your yard, or some other object. A dog who exhibits possession aggression may growl if someone approaches his food bowl or goes near him when he's chewing a favorite toy. He may bite a stranger who steps into your home. The degree of aggression can vary from dog to dog and between objects. For instance, a dog might not care if you sit next to him and pet him while he chews a rubber toy, but may turn and snap at you when you do the same thing while he chews a pig's ear.

Frustration

Aggression that is caused by frustration is often referred to as redirected aggression or barrier frustration. It occurs when a dog is frustrated at not being able to get to something, and he takes the frustration out in another way. An example of this is a dog who is tied in the yard and spends the day straining and trying to get to a dog that lives across the street. The dog will usually bark and growl as his frustration grows. When his owner comes to bring him in, the dog redirects his frustration and bites the owner. This type of aggression is often seen in dogs who spend a lot of time tied out, restrained on a leash, or behind a chain link fence.