Aggression Toward People (Dogs)

Why Dogs Act Aggressively

Aggression is the most serious behavior problem in dogs and is unfortunately quite common. It’s a symptom of an underlying problem and it always needs to be taken seriously. Aggressive behavior can be seen in dogs of any breed, size, age, and gender, and it can spring from many different motivations. The most common include:

  • Fear/defense
  • Pain/discomfort
  • Possessiveness
  • Territoriality
  • Redirected

What Aggression Looks Like

  • Still, rigid body
  • Stiff and high tail that slowly wags (like a rattle snake giving warning)
  • Direct stare
  • Deep-throated, threatening bark
  • Lunging or charging at someone
  • Growling, snarling, baring of teeth
  • Snapping, nipping
  • Biting, shaking

Even mild forms of aggression, when not properly addressed or inappropriately punished, can evolve into serious aggression. This is why it’s important to immediately assess and tackle any change in your dog’s behavior. To address aggression, you should work with a professional that looks at the context in which it happens and does not use a punishment based approach.

 Aggression toward Strangers

When a dog is uncomfortable around strangers, or certain strangers (such as men, kids or uniformed people), it’s usually because he hasn’t been fully socialized. A well-socialized dog is relaxed in his environment. However, in order to become socialized, a dog must have sufficient exposure with positive experiences, especially when young. Aggression comes into the picture when the dog encounters something he isn’t accustomed to and tries to make the “scary” person flee by behaving aggressively. The underlying motivation is fear. (The stranger may be a kind, gentle person; this is irrelevant to an under-socialized dog.)

Aggression toward Family

When dogs threaten or bite family members, the number one reason is fear. This is the case especially when reached for or touched, even when it seems the dog’s behavior is offensive. Other possible explanations include object guarding (possessiveness), handling issues (discomfort/pain/frustration).

Possessiveness of food, toys, and sleeping locations is common in pet dogs. They might get snarly about anything from food dishes and bones, to sofas and beds, even tissues and garbage! Handling issues are also common. Many dogs are naturally reluctant to have their bodies touched or manipulated in certain places or in certain ways. If these dogs are not taught to accept and enjoy handling and surrendering valuable items, they may threaten or bite in this context.

What You Can Do

First, see your vet. Aggression may stem from an underlying medical issue causing your dog pain, discomfort, anxiety, insecurity or confusion. Your first call should always be to your vet to rule out a variety of conditions, from arthritis to cognitive dysfunction.

Practice avoidance. Initially do your best to avoid anything that triggers the aggression in your dog. In most cases it is best to seek help from a professional and address the aggression with a treatment plan in a non-confrontational way. You may need to cross the street, put your dog in a separate room when friends come over, feed your dog alone in a separate room, or avoid certain toys altogether.

Use management tools. Tools can help you manage aggression problems. In your home, you can use baby gates to restrict your dog’s access to problem areas. A head halter or harness makes on-leash management much easier. A basket muzzle, if it can be introduced to your dog safely, for example, will prevent your dog from biting, but still allows him to pant and drink water.

Punishment is rarely the answer.  All types of aggression can get worse through badly timed or poorly applied punishment. For more information about this, read the American Veterinary Society of Animal Behavior’s position statement on punishment at

Get professional help. Aggression can be dangerous, especially when directed at children. For a well-designed behavior modification plan always seek help from a qualified professional. At SF SPCA, contact our board-certified veterinary behavior specialist Dr. Berger. Don’t live in the Bay Area? Search locally for a veterinary behavior specialist (Dip ACVB), a Certified Applied Animal Behaviorist (CAAB or ACAAB), or a Certified Professional Dog Trainer (CPDT).


  • If you haven’t done so already, spay or neuter your dog.


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