Understanding Reactivity in Dogs: The Instinctual Response to Threats

Dogs often react suddenly and intensely to certain situations, leaving their owners puzzled or concerned. This behaviour, known as reactivity, is an instinctual action triggered by an external stimulus. It happens quickly and without deeper thought, driven by the dog's survival instincts. Understanding what reactivity is, what causes it, and how it works in the dog's body can help owners manage and support their dogs better.

What Reactivity Means in Dogs

Reactivity is an immediate, instinctual response to something the dog perceives as a threat or challenge. Unlike calm or thoughtful behaviour, reactive responses happen without the dog pausing to think or analyse the situation. This reaction is often loud, fast, and intense, such as barking, lunging, or growling.

It’s important to distinguish reactivity from aggression. Reactivity is about the dog's instinct to survive and protect itself, not necessarily about wanting to harm. The dog’s brain is flooded with stress hormones, and it acts purely on impulse.

The Difference Between Fear and Anxiety in Dogs

Fear and anxiety are related but distinct emotions that influence reactivity:

• Fear happens when a dog faces an actual, immediate threat. For example, a dog might bark loudly and lunge if a stranger suddenly approaches aggressively. This reaction is sudden and dramatic.

  
  

• Anxiety is the anticipation of a threat that might happen in the future. A dog might show signs of stress or nervousness before a vet visit or during a thunderstorm. This response is usually slower and lasts longer.

  
  

Understanding this difference helps owners recognise whether their dog is reacting to something present or worrying about what might happen.

What Causes Reactivity in Dogs

Several factors contribute to why some dogs are more reactive than others:

• Genetics and Epigenetics

Some dogs inherit a natural tendency toward reactivity. If a mother dog experiences stress during pregnancy, the stress hormone cortisol passes through the placenta to the puppies. These puppies are born ready to face a stressful world and may be more prone to reactive behaviour.

• Lack of Controlled Socialization

Puppies that miss out on safe, positive social experiences during early development may grow up fearful or reactive around new people, animals, or environments.

• Traumatic Experiences

Negative or frightening events can cause a dog to develop reactivity as a defense mechanism.

• Single Event Learning

Sometimes, one bad experience is enough to trigger a lasting reactive response to similar situations.

How the Body Reacts to Threats

When a dog senses a real or perceived threat, its body reacts immediately through a complex process:

1. Amygdala Activation

   The amygdala, a part of the brain that processes emotions like fear and pleasure, activates first. It triggers the release of stress hormones such as adrenaline and cortisol.

   
   

2. Sympathetic Nervous System Response

   This system prepares the dog for fight or flight. Pupils dilate, heart rate and blood pressure increase, and breathing speeds up.

   
   

3. Energy Release

   Glucose floods the bloodstream, providing energy for the dog to respond quickly.

   
   

4. Non-Essential Systems Slow Down

   Systems like digestion slow down because the body focuses on survival.

   
   

At this point, the dog's brain is no longer engaged in learning, they are only thinking about how to survive the next few minutes, and stress hormones flooding their internal systems cause behavioural reactions e.g., lunging, barking and growling. The dog reacts purely on instinct to survive the moment.

How Reactivity Is Regulated

The hippocampus in the prefrontal cortex helps regulate this response. It evaluates whether the threat is still present and signals the body to calm down if the danger has passed. However, if the hippocampus is overwhelmed or the dog has had traumatic experiences, this regulation may not work well, leading to prolonged or exaggerated reactivity.

Practical Tips for Preventing and Managing Reactivity

Understanding reactivity helps owners take steps to support their dogs:

• Early Socialization

Introduce puppies to a variety of safe, positive experiences and calm controlled interactions with other dogs to build confidence.

• Calm Exposure through counter conditioning and desensitisation

Desensitisation is the gradually exposure of triggers at a distance where the dog feels safe and is under threshold (non reactive and calm). It is here we use counter conditioning to change the dog's emotional response to the trigger by creating an association with the trigger and something positive. We do this by having them at that safe distance from the trigger so they are under threshold but still able to see the trigger and reward using high value food for remaining calm.

over time you can gradually reduce the distance between the dog and the trigger, until they are able to calmly walk past without being fearful and reactive.

• Stress Reduction

You can use activities such as sniffing and chewing by providing snuffle mats and chew toys/bones to help calm your dog, both are natural behaviours that all dogs enjoy and trigger the release of feel good hormones, helping to relieve stress and anxiety. Provide your dog with plenty of enrichment to prevent frustration and promote calm.

• Professional Help

Work with trainers or behaviourists who understand reactivity and can design tailored plans.

• Avoid Punishment

Punishing reactive behaviour increase fear and stress, making reactivity worse.

Why Reactivity Is Not a Choice

It’s easy to think a dog is being “naughty” or stubborn when it reacts suddenly. In reality, reactivity is an automatic survival response. The dog’s brain is flooded with hormones, and it cannot pause to think or reason. This instinctual behaviour is about staying safe, not about disobedience.

Owners who understand this can approach their dogs with more patience and empathy, focusing on support rather than blame.