Why Do Dogs Become Reactive



Have you ever taken Fido for a walk only to have him turn into a snarling beast at the sight of a nearby dog? Does your dog's crazed barking at the mailman nearly drive you around the bend? If so, you are not alone. What causes our normally sedate canine companions to suddenly turn into the canine equivalent of Jaws? Reactive behavior often takes us by surprise, but the reality is a reactive outburst is nearly always precipitated by warning signs. What causes reactivity in dogs? It's a complex question. The truth is, there are a number of triggers which can elicit an over the top response from our dogs. While reactive behavior is easy to spot, it isn't always as easy to determine the factors that lead up to it. There is no doubt that a reactive dog is struggling and needs help from his loving, compassionate owner. What is reactivity and what causes it? What can we as owners do to help our beloved dogs with the things that trouble them?

The Root of the Behavior

Reactivity is just that; a reaction to something upsetting to your dog. The reactive response can come in many different forms. For some dogs, it is lunging and barking; for others, it may be whining, pacing, panting, or even hard staring. Though the reaction may differ from dog to dog, what does not differ is the fact that your dog is having a very hard time. When your normally calm and civilized dog has an outburst, you can be left feeling embarrassed, frustrated, and downright shocked. Most owners report that they didn't see the behavior coming and were taken completely off guard. Some become frightened and question the soundness of their dogs' temperaments or even if the dog should be put down. 

When a dog has a reactive response to something, we begin to draw parallels, and we often make tremendous leaps in logic. We wonder if our dog will lunge and bark aggressively at a child on a bicycle, would he actually bite a child if given opportunity? Would the dog that races up and down the fence in your yard kill the little dog attempting to bite him through the fence if given the chance? We imagine the worst possible scenarios in our minds, and we torture ourselves because we love Fido, but at the same time, we feel responsible to keep him and the people we encounter safe. Reactive behavior calls into question our ability to do that. The truth is, we often overthink this. Reactive behavior is quite normal in canines. We must remember first and foremost that canines lived in the wild before cohabiting with man. We have taken an animal intended for a life of survival of the fittest and attempted to turn him into a glorified house pet expected to follow and obey even the subtlest of our household rules, and all of this without a road map; without the ability to speak to communicate his own needs and desires. We expect a lot from our dogs. Sometimes, living in harmony in the domesticated world is very hard for our dogs, and at these times, we see reactivity emerge. Many people mistake reactivity for aggression. Though they can look the same, they are quite different beasts. Reactive behavior is a negative response to something that causes fear, anxiety, or stress in our dogs. When your dog displays reactive behavior, his goal is singular. He wants whatever it is that is causing him to feel ill at ease to GET AWAY.

So, if reactivity is not necessarily linked to a poor temperament, what causes some dogs to be reactive while others are not? There are many different factors that could be at play in producing a dog who is more likely to respond reactively to various upsetting stimuli. In general, researchers agree that genetics play a large part. If Momma or Poppa was a reactive dog, Junior will likely exhibit this behavior as well. Why? The canine temperament is greatly affected by genetics, but it is also shaped by observation. During a dog's first twelve weeks of life when the most critical socialization is being done, your dog is learning how to relate to his world by observing the other dogs around him. That combined with his genetics will lay the foundation for who your dog will become and how he will respond to future events. This is why it cannot be overstated that a puppy should only be exposed to things that are safe, and that will build positive experiences for him. During peak fear periods, even one negative incident can have a lifelong impact on a dog and his ability to respond appropriately to his world. 

Encouraging the Behavior

Hormones also can affect reactivity. A normally happy, well-adjusted male dog can have a seemingly extreme reaction to another male dog approaching a female in his home that is in heat. So too can a gentle-natured, loving female dog suddenly snap at a male dog that tries to mount her or even a female that tries to come near her young. It is an instinctive hormonal response instilled in our dogs for their protection. Sometimes reactivity can be a working out of pent-up frustration. This is often seen in leash reactivity. You take Fido for a long-anticipated walk, and you see a dog coming towards you on the horizon. Fido's tail slowly begins to wag, his eyes get a little glassy, and his panting is more labored. He's excited! Yet, as the dog gets nearer and nearer, he lunges on his lead, begins to whine, and even bark a little. By the time the dog is nearby, Fido's excitement appears to have turned a corner into a darker zone. He's pulling you strongly towards the other dog, and you're not sure that you can hold him back much longer. Suddenly, there is an explosion of loud, aggressive-sounding barking, and you know you have to get you and Fido out of the situation as quickly as you can. 

What just happened? Fido's excitement crossed the threshold into overexcitement and without the tools to properly calm himself, he gave in to a reactive response to provide an important release. Overarousal can very quickly turn into aggressive behavior if not interrupted and redirected when given preliminary signs. This is exceptionally dangerous, and care must be taken to never allow your dog to remain in this state for long. The results can be disastrous and permanent. All it takes is one unfortunate incident to scar a dog for life. 

Other Solutions and Considerations

Reactivity is never something to be taken lightly. There are two routes for addressing the problem. The first is management. Management involves removing the items that are triggers from your dog's daily routine. This is an effective strategy except you cannot control everything that comes into Fido's life. Life is full of surprises, and unfortunately, when it comes to reactive dogs, they are not always pleasant. Management is important, but we must always remember that even the best-laid plans will sometimes fail. Management alone will not be a powerful enough tool to assist with rehabilitating a reactive dog. The second approach is training. Training must be coupled with management in order to be the most effective. The best outcomes are achieved through redirection, counterconditioning, and desensitization. All of these techniques take time and a great deal of patience, but it is critical for our dogs to learn new and more acceptable methods of coping with their emotions. During the course of training, you will experience progress and then setbacks. It is a long road to rehabilitation, and it should never be attempted alone. If you have a reactive dog on your hands, it is critical that you consult a reputable behavior modification trainer with expertise in dealing with reactive dogs to assist you on your journey. Your dog's well-being and safety are at stake. There is hope, but you need help. This is not something that you can or should do alone. 


Dog reactivity is a common phenomenon in the dog world. It can be frightening and embarrassing for us as owners, but it is a powerful communication tool our dogs use to let us know when they are afraid, anxious, or even hurting. Take the time to understand your dog and your triggers then enlist the help of a great trainer to help Fido learn that the world truly is a great place after all!