Whether it is directed towards you or another family member, a stranger, or another animal, an aggressive dog can not only be very frightening but may also lead to injury or legal action. But although it may seem like your dog is biting you aggressively or showing other aggressive behaviors out of the blue, most dogs only exhibit aggressive behavior for a few basic reasons: they're sick, frightened, possessive, or frustrated.

Understanding why your dog is biting, growling, or showing other aggressive actions is the first step in resolving this potentially dangerous behavior. Too many owners assume that an aggressive dog is out of control and must be rehomed or euthanized. However, once you take steps to resolve the situations causing your dog to act out, you'll often find that the aggression disappears or is greatly reduced.

Here's what you need to know if your dog is getting aggressive with you, family members, pets, or strangers.

Signs of Aggression in Dogs

First, however, it helps to know the signs of canine aggression, as few dogs bite without first showing escalating behaviors that indicate an attack is coming. A dog displaying aggression may:

• Stand very still with a rigid posture
• Make direct eye contact and hold it
• Flatten the ears against the head
• Growl or bark in a threatening tone
• Snarl
• Curl its lips to expose its teeth
• Lunge forward without making contact
• Snap without making contact
• Bite lightly so as not to break the skin
• Bite hard enough to break the skin or leave a mark

Depending on the cause and intensity of the stimulus provoking the aggression, a dog might progress through all of these behaviors, or might just deliver a warning by growling, snarling, showing aggressive body postures, or exposing teeth without progressing to an actual bite.

Why Do Dogs Show Aggression?

Knowing why your dog is acting aggressively can help you make the best plan for stopping this frightening behavior. Most often, your dog will display aggression for one or more of the following reasons:

Illness and Injury

Some medical conditions can cause dogs to become aggressive. If a dog that has never shown any sign of aggression suddenly begins growling, snapping, or biting, it may be caused by a disease or illness.

Pain is an especially common cause of aggression in dogs. Your suddenly aggressive dog may have an injury or an illness that's causing major discomfort and stress. Some possible causes of pain include arthritis, bone fractures, injuries, and tumors.

Other illnesses may affect your dog's brain, leading to aggression that seems unreasonable. Conditions such as cognitive dysfunction, brain tumors, and other brain diseases may cause the onset of aggression. These problems are more likely to occur in older dogs but can happen at any age.

If your dog is exhibiting sudden, unexplained aggression, talk to your veterinarian before attempting to address it as a behavior problem.

Fear

A fearful dog can easily develop aggressive behavior. Most dogs only exhibit aggressive behavior if they sense that they are in danger, cannot escape, and feel the need to defend themselves. For example, this may occur if a dog is backed into a corner with no way out, or if it thinks a hand raised over its head means it is going to get hit.

If your dog is a rescue dog that exhibits more aggressive or fearful behavior than is normal, it may have been abused, neglected, experienced a traumatic event, or not properly socialized as a puppy. Any information you can get from the organization where you adopted the dog could help you determine the best way to handle the situation.

Sometimes rescue dogs need obedience training with an instructor who specializes in teaching dogs that have been abused or those that have not been properly socialized. In some cases, you may be able to manage your dog's fear on your own with training and patience. You can speak to a veterinarian about the best course of action.

To avoid provoking this type of aggressive behavior, approach unknown dogs carefully (better yet, let them approach you). Train and socialize your dog to help prevent fear down the road.

Possessiveness

Possession aggression, or resource guarding, occurs when a dog is possessive of something. This is often food, toys, or some other object of value. A dog that exhibits possession aggression may growl if someone approaches his food bowl or gets too close when he is chewing a favorite toy.

A dog may also bite or show aggression to a stranger who steps into your home or onto your property, which is the dog's territory. This is a common scenario with dogs who "hate the mail carrier" or bark violently at people just outside the property boundary or fence.

Resource guarding is also a common cause of aggression towards other household pets. Some dogs will growl, snap, or bite other animals in the home who approach the dog's food bowl, bed, or favorite toy.

The degree of aggression may vary from one dog to another and between objects. For instance, your dog might not care if you sit down and pet him while he chews a rubber toy, but he may turn and snap at you when you do the same thing while he gnaws on a dental chew. It all depends on the value that the dog attributes to each object or resource.

Frustration

Aggression that's 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 takes its frustration out in another way. This type of aggression is common in dogs that spend a lot of time tied up, restrained on a leash, or behind a chain-link fence.

For example, a dog that's chained in a yard may spend the day straining to get to a dog that lives across the street or in an adjacent yard. The restrained dog usually barks and growls more fiercely as the frustration grows. When the owner approaches, the dog may redirect its frustration and bite the owner. Redirected aggression may also result in the dog lashing out at another family pet, whether canine or feline.

What to Do If Your Dog is Showing Aggression

Be careful not to misinterpret your dog's aggression. Always see your veterinarian to rule out a health or behavioral issue before you assume you know the reason for your dog's aggressive behavior. Otherwise, attempts at corrective measures could make the problem worse.

You may be tempted to try giving your dog medication to relieve pain or calm them down, but this is something you should not do. If your dog is unwell, you'll need to know exactly what is wrong before starting any treatment. Only a veterinarian can advise what medications are appropriate for your dog.

If your vet has ruled out medical issues and you still can't get to the root of your dog's aggression, it can help to consult a professional. Find a dog trainer or behaviorist who specializes in canine aggression. These specialists have knowledge and training methods that can be very effective even with dogs that seem to be "lost causes."