Aggression is a normal form of communication for animals and a common life-threatening behavior problem in pets. The problem is not only dangerous for humans or other animals to which the aggression is directed, but left unresolved, aggression is a common reason for pets to be euthanized.

Staring, growling, hissing, lunging, snapping, swatting, and biting are all behaviors described as aggression. Many conflicting opinions and misinformation can be found online, on television, and in books describing the motivations behind aggressive behaviors. However, scientific research tells us that fear, anxiety, and pain are often the most common reasons why animals will use aggression.

Getting Started

When an animal first shows aggression, a thorough physical exam, neurologic exam, and orthopedic exam by a veterinarian will help to rule out underlying medical conditions that may be stimulating the aggressive behavior. A complete blood count, serum biochemistry profile, and urinalysis help to evaluate organ function along with a thyroid profile if supported by other findings, to rule out hypothyroidism in dogs and hyperthyroidism in cats.

Troubleshooting Beforehand

Safety is a top priority when living with or working with aggressive animals. Identifying and avoiding the triggers for aggression when possible will reduce the opportunity to practice the behaviors and help your pet feel safe. Recognizing body language cues of fear, anxiety, and stress such as ears back and flat against the head, head down, tail tucked, lips tight and drawn back, leaning away or crouched position, avoiding direct eye contact, licking of the lips, yawning, dilated pupils, and hair standing up (piloerection) will help to increase safety when you recognize these and indicators of a potential aggression response from your pet. Many people are under the misimpression that a dog wagging its tail is happy; this is not true. Tail wagging actually signals a willingness of the dog to interact, be that through happy interactions like play or petting, or in the case of an aggressive animal, through biting.


Treating aggression can be challenging, and often these animals are not cured, but rather managed; it all depends on the underlying motivation.

  1. The procedures below can be helpful, but they do not replace expert help for an individual animal. Contact your veterinarian for referral either to a trained veterinary behaviorist, or to a reputable animal trainer. This is important because many so-called trainers are not actually equipped to help, and some recommendations can be counterproductive.
  2. The first step of treatment often involves increasing human safety by teaching the dog to wear a basket muzzle (Baskerville or Italian Basket Muzzle; see Figures 1 and 2). If desensitized and counter conditioned properly, dogs can learn to love wearing a muzzle. Some will even ask to put it on. The openness of the basket helps to reduce severity of bites and allows delivery of treats during training and behavior modification sessions.

  3. Identifying potential triggers and avoiding them or the use of desensitizing and counterconditioning to reduce fear associated with these triggers can also be of value.

  4. Dogs and cats can react to a variety of different triggers such as other dogs, other cats, certain people, children, noises, bicycles, cars, and situations. For the dog that is aggressive to visitors, putting the dog away in a crate or behind a closed door with a yummy treat such as a food-stuffed Kong or puzzle toy will help remove the dog from situations that make him or her uncomfortable. The long-lasting treat or toy helps to condition the dog to form more pleasurable or positive associations with visitors.

  5. For dogs and cats aggressive to other cats in the household, separation is key to managing and reducing aggression.

  6. For dogs that are aggressive to other dogs on and off leash, avoiding dog parks or walking the dog in a location where other dogs are rarely present may be required. Teaching the dog to “look” or “watch” you (eye contact) instead of the other dog or person on walks will help to redirect the dog and when paired with yummy treats, form more positive associations with these triggers.

  7. Tools such as head collars and front clip harnesses give you better control of your dog on walks and help redirect your dog’s focus away from the trigger as he or she continues to move on past. These can also be used in the house attached to a 6- or 4-foot (2- or 1.3-meter) leash if needed for extra safety. Retractable leashes should never be used with an aggressive dog of any size: they provide no control and can be scary if dropped or snapped.

  8. For cats and dogs, positive reinforcement training is excellent for improving communication and teaching behaviors used for redirection in a nonconfrontational way.

  9. In the house, dogs and cats can be taught to stay on a mat for various periods of time. This mat is a very useful place to redirect your pet if you notice behaviors indicating an impending fight between household pets or if your pet needs to be safely removed from the couch, chair, or bed without confrontation.


Punishment in the form of shock collars, water bottles, cans of pennies, alpha rolls, spanking, or even just yelling “no” is often counterproductive with aggression. It is much more effective to teach and reward your pet for acceptable behavior than it is punishing the ones you do not desire. The use of corrections can confuse and frustrate dogs and cats, making them more fearful or anxious and increasing the likelihood that they will bite.

As with other behaviors, early detection and intervention are crucial in the management and treatment of aggression. Early socialization along with fun and pleasurable interactions with humans and other animals will help dogs and cats experience less fear or anxiety when presented with novel stimuli in their environment. It gives them the opportunity to form better coping skills.

Basket muzzle seen from the dog’s perspective. The open spaces allow breathing and make the muzzle comfortable.
Basket muzzle being placed on a dog. Note the open spaces that allow the tongue to pass through and receive a treat.

Frequently Asked Questions

Are medications available to modify my pet’s aggression?

Medications are available to modify some behaviors and should be used only in conjunction with a complete behavior modification program under the direction of a veterinarian. Contact your veterinarian for further guidance.

Can my pet’s aggression become worse over time?

Yes. This is why it is important to identify triggers that, without your knowledge, may be triggering aggression. By managing your pet’s environment and preventing exposure to triggers, aggression is less likely to occur.

Is there ever a time when a repeatedly aggressive dog or cat can be considered cured of his/her aggression?

Unfortunately, an animal that is aggressive is never considered cured. However, with proper management, safety improves for all involved. Early intervention and an understanding of body language cues reduces the risk of human injury or self-injury.

What are the circumstances where a simple punishment should help to correct aggressive behavior?

None. Research shows us that punishment is likely to increase fear, anxiety, and aggression.


Christine D. Calder, DVM, DACVB

Source: From Cohn and Côté: Clinical Veterinary Advisor, 4th edition. Copyright © 2020 by Elsevier Inc. All rights reserved



Aggression can be a normal behavior in dogs and cats. Cats and dogs in pain, frightened, stressed, or under duress often show signs of aggression. However, aggression that occurs with some regularity toward known or unfamiliar people or dogs/cats may be abnormal and problematic for both the patient and people. Aggressive dogs and cats are dangerous to themselves and others, yet many have a treatable behavioral pathology. Early intervention is always best because it will always involve the simplest treatment.

Often, aggression is a sign of anxiety and distress that is best addressed by either your veterinarian or a specialist in veterinary behavioral medicine working with you as the pet owner. Remember, the owners of aggressive pets are ethically and legally liable for their pets’ aggression. Clients should ask their veterinarians for an assessment and help at the first signs of any concerning or aggressive behavior. Treatment usually involves some environmental changes, behavioral interventions and treatment, and medication that will decrease anxiety and help the patient to acquire new behaviors more easily.


There are several recognized classes of aggression in dogs:•Impulse control aggression (sometimes called conflict aggression)involves aggression to people by dogs when the dog perceives that humans attempt to control the dog’s behavior or access to the behavior. These dogs dislike manipulation (for example, including being pushed from furniture, disturbed while sleeping, etc.). These dogs are anxious and attempt to control all interactions as a way of controlling their anxiety.

  • Territorial aggression involves dogs that forbid access to an area they feel they must protect. Most dogs will exhibit some protective responses to houses, properties, et cetera. Dogs with territorial aggression forbid access regardless of the context and the behavior of the person approaching. Furthermore, the response of the individual approaching may not matter if they are near the boundary—the affected dog reacts profoundly, regardless.
  • Anxious dogs become aggressive if they perceive risk. Fearful dogs choose to withdraw and not participate in social situations. If they can’t get far enough away from someone worrisome to them, these dogs will exhibit some or all of the behaviors associated with both fear and aggression: piloerection (hackles raised up), growling, snarling, staring, lunging, and biting, which usually occurs as someone moves. Dogs who bite when fearfully aggressive tend to do so from behind and may then withdraw after biting. For these dogs, biting is a last resort. If such dogs continue to be or feel threatened they will bite earlier in the sequence.
  • Food aggression describes dogs that react aggressively in the presence of food, when anticipating food, or when food is taken from them. This aggression could be directed at humans or at other animals. Some dogs will guard only what they perceive as valuable food items (e.g., real bones). The easiest and safest way to handle these dogs is to feed them undisturbed, behind a gate or door if needed, and only offer them special foods when they can be left to enjoy them unmolested.
  • True interdog aggression involves more than squabbling. This diagnosis can indicate a serious pathology when one dog will not tolerate the presence of another dog (or dogs, which is less common). It almost always involves dogs going through social maturity who are changing their social behaviors


  • The safety of humans and other animals is paramount. Accordingly, seek the help of your veterinarian immediately if your pet shows any signs of aggression. If your veterinarian feels that the behavioral problem is beyond the scope of his or her competence, referral to a specialist in veterinary behavioral medicine (in the US: or or a veterinarian with a special interest in behavior ( may be recommended.


Treatment requires expert help. The information here is general and is not adequate to deal with most aggressive pets. Seek help early!

  • There are many tools that can make it easier to manage the behavior of dogs and cats. All such tools must be used in a humane fashion – harnesses, head collars (dogs), and Sherpa bags are very helpful. Tools such as shock collars and prong collars are to be avoided. No device that relies on force, fear, or pain should ever be used (;;
  • Avoid situations likely to cause an aggressive reaction. Avoidance will keep everyone safe and will minimize practice of the pathologic behavior.
  • Simple training is not sufficient to treat pathological behaviors. Most certified, positive trainers now can recognize when behaviors will benefit from specialist intervention and are often willing to work with you and your veterinarian and/or specialist as part of the treatment. Behavioral and environmental modification will need to be geared to each unique animal, diagnosis, and settings.
  • Reward normal/good behavior but never punish the pathologic behavior. Veterinarians and specialists can help with this and may include in the treatment team a trainer who uses only positive methods and has special training to help with distressed dogs and cats. Not only does punishment increase the risk of aggression, but it tells the cat or dog only what you do not want them to do. To improve, cats and dogs need to know what behaviors will be rewarded and what behaviors will help them to feel calmer and happier.
  • Medication is a common component of treatment because all double-blind, placebo-controlled studies in companion animals have shown that patients taking medication acquire new behaviors taught through behavior modification more quickly. Premedication blood testing to assess medical risk is always recommended. Routine follow-up will involve repeated laboratory testing if treatment continues.
  • Remember that pain can cause aggression as a normal behavior. While most behavioral problems are not due to a medical problem, some are, which is why it is essential that you start by consulting your veterinarian. Furthermore, if your dog or cat becomes physically ill, this will often worsen a behavioral problem
  • The goals of treatment are to keep everyone safe, improve the patient’s quality of life and welfare, and ensure a happier household overall. Stressed and distressed cats and dogs do not have good mental health, and the preservation of mental health is at the core of behavioral medicine.
    AUTHOR: Karen L. Overall, MA, VMD, PhD, DACVB


From Cohn and Côté: Clinical Veterinary Advisor, 4th edition. Copyright © 2020 by Elsevier Inc. All rights reserved


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