Why Do Dogs Shake When Scared?

Adrienne F.

If you have ever seen dogs shake when scared, you may be wondering what's going on. Let's take a look at some dynamics.

If you have ever seen dogs shake when scared, such as when a summer storm is rolling in, or when you're taking your dog to the groomer or the vet's office, you may be wondering what's behind all that shaking. Sure, it's pretty clear that the anxiety or fear are the underlying emotions triggering shaking in dogs in certain contexts, but what is really happening at a physiological level? Why do dogs shake when scared? It's surely interesting discovering what's presumably going on internally, so let's take a closer look at the exact mechanics.

A Matter of Adrenaline

When dogs are exposed to events that are perceived as anxiety-inducing or very exciting, their bodies start releasing adrenaline. Adrenaline, also known as epinephrine, is a key hormone that's responsible for preparing the body for the "fight or flight" response.

The fight or flight response is simply a physiological reaction (in other words, something that is not under conscious control) that occurs when an animal or human feels threatened. It's the "attack or run" instinct reminiscent of times when predators abounded. Today, this response still comes handy whether being at risk of being run over by a car or kicked by a horse.

The first person to describe the fight or flight phenomenon was American psychologist Walter Cannon in 1920. This chain reaction, (which is triggered by the sympathetic nervous system) starts in the dog's amygdala which ,triggers the pituitary gland to activate, leading to a sudden release of hormones and neurotransmitters such as cortisone (a metabolite of cortisol), adrenaline and noradrenaline (a neurotransmitter) into the bloodstream.

The surge of all these chemicals acts almost instantaneously in a well-choreographed manner throughout the dog's body. What happens though exactly? More specifically, the dog's body undergoes several physiological changes including: increased heart rate, increased breathing, increased blood pressure, increased muscle tension, increased blood clotting, increased blood sugar (being diverted from the blood to the muscles) and increased awareness.

Why Do Dogs Shake When Scared or Excited?

All of the above described physiological changes occurring when a dog is in a fight or flight response are meant to cause responses in the body to increase the ability to survive.

The increased heart rate sends oxygen, and therefore, increased blood flow to the muscles so dogs can sprint into action at a moment's notice, the increased awareness causes the senses to heighten so to readily spot enemies (pupils dilate to help scan the environment), the increased blood clotting ability helps prevent excessive blood loss.

When it comes to shaking, this is also presumably a result of the fight and flight response. The shaking is a byproduct of the readiness of the major muscles to expend energy. With blood flowing to the large muscles and the muscles becoming tense, dogs are more ready for fleeing or attacking.

However, if fleeing or attacking doesn't take place, the muscles can't remain in a perpetual "spring loaded" state and the excess energy must go somewhere. All this excess energy release results in fidgeting, twitching or shaking. Hence the sayings: "to shake in fear" or " to tremble like a leaf."

Helping the Shaking Dog

It's often tempting to help the shaking dog feel better, but what can be done? You can't really rationally talk dogs through their fears and explain to them that there is nothing to worry about. And asking the dog to "chill" by demanding him or her to sit or lie down on a mat to relax, won't cut it: dogs in a fearful state don't do well being kept immobile.

It's like asking yourself to sit calm and still when you are angry and just need to flap your arms, walk up and down and gesture, explain Martina Scholz and Clarissa von Reinhardt in the book "Stress in Dogs: Learn How Dogs Show Stress and What You Can Do to Help."

A better option instead is to provide the dog with the opportunity to move so to loosen those tight muscles and release the energy. So next time your dog is shaking at the vet, rather than keeping your pup in your lap or asking him to sit, try taking him outside to stretch his legs and sniff around. As veterinarian and Professor Emeritus Dr. Robert Hamlin puts it, goes a long way, he claims "The only time a sympathetic storm is good for you, is to fight or flee."

On top of this, of course, it would also help a lot putting some effort in making the event less stressful so to prevent shaking episodes from occurring in the first place. So if your dog literally shakes during vet visits, consider helping your dog feel less tense and help him overcome his White Coat Syndrome with pleasant experiences. You can do so through by exercising your dog prior to his vet visit, investing in some calming aids, and making the vet visits as less stress-free as possible by taking your dog to practices that are Fear-Free Certified.

"The main reason a stressed dog should never be forced to carry out "sit" and "down" commands is that it takes away the possibility for dogs to use movement to loosen and relax his tense muscles. Movement is essential during times of stress-in humans and in animals. If the dog doesn't have the chance to move, it could result in trembling or even in painful muscle cramps, which then lead to greater readiness for aggression."~Martina Scholz, Clarissa von Reinhardt

A State of Homeostasis

While the sympathetic nervous system is responsible for kicking the fight or flight response into gear during perceived dangers, the parasympathetic nervous system plays a totally opposing role. Its main responsibility being restoring the dog's body in a state of homeostasis.

What exactly is homeostasis? Those who studied biology at some point in their lives might recall this term, which simply describes a state of normalcy. The concept is that the body has an ideal level of oxygen, an ideal level of acidity, an ideal level of glucose, an ideal level temperature etc.. Stress can be defined as a disruption that throws the body out of homeostatic balance. When things go topsy-turvy, therefore, the body aims to restore to a state of normalcy, basically, homeostasis.

So in instances when the body is in a state of fight or flight with the sympathetic nervous system activated at full gear, after a while, the parasympathetic component kicks in and mediates calm, slowing down the heart rate, lowering blood pressure and inducing a state of relaxation. The sympathetic storm is now finally over.

Did you know? Even after the nervous system has stopped responding, it is normal to feel somewhat "on edge" for a while. This is because the chemicals are still floating around for some time and there is an adaptive reason behind this: in the wild, dangers have a tendency to return (the wild animal may catch up again) and it's productive for the nervous system to be able to re-activate again quickly.

Disclaimer: this article is not meant to be used for diagnostic purposes or as a substitute for professional veterinary or behavioral advice.


  • Mastery of Your Anxiety and Panic By David H. Barlow, Michelle G. Craske
  • Why Zebras Don't Get Ulcers, Robert M. Salposky 1994 W.H. Freeman and Company
Comments (2)
No. 1-1

I wish dogs didn't ever get scared. poor things!

1 Reply

Adrienne Farricelli CPDT-KA
Adrienne Farricelli CPDT-KA


I wished so too, and it's not like we can rationally talk them through their fears to help them understand there's nothing to fear.