Understanding Reactivity in Dogs
Reactivity is one of the most frequently encountered behaviour challenges and one that causes significant confusion. Many assume that a reactive dog is simply “badly trained” or “behaving badly,” but reactivity is not a label or a character trait. It is a behavioural expression of emotional overload, driven by the dog’s nervous system and shaped by genetics, learning, environment, and health.
When we begin to look beneath the outward barking or lunging, the underlying emotional processes become clear. Reactivity is not about control or dominance; it is about a dog who can no longer regulate their arousal in the presence of a trigger.
What Reactivity Really Is
A reactive dog is one who responds quickly and intensely to external stimuli. The response might involve barking, lunging, whining, freezing, pulling away, or redirecting onto nearby objects or people. These behaviours are not deliberate attempts to be difficult. They are signs that the dog’s threshold has been exceeded and that their emotional state has shifted into survival mode.
This shift is almost always limbic-driven. When the amygdala detects something it perceives as threatening or overwhelming, it activates the sympathetic nervous system before the prefrontal cortex has the opportunity to process information. This means reactive behaviour is often reflexive, not cognitive.
This explains why trained cues frequently fail in reactive moments. A dog cannot access learned behaviours when the survival centres of the brain are dominant.
The Neurobiology Behind Reactivity
Reactivity is fundamentally a neurobiological event. The amygdala triggers the release of adrenaline and cortisol, increasing arousal and preparing the dog for action. During this state, heart rate increases, attention narrows, and behavioural responses become rapid and intense. Once these stress hormones are circulating, they do not clear immediately. This contributes to stress stacking, where each arousing event primes the dog to react more strongly to the next one.
Understanding this process helps us interpret behaviour with far more accuracy. A dog who is still recovering from a previous stressor may appear to react “out of nowhere,” when in fact the nervous system was already primed for activation.
Why Some Dogs Become Reactive
Every dog has a unique combination of genetic predispositions, early life experiences, health status, and environmental influences. Some dogs are naturally more alert, sensitive, or excitable, while others may have had insufficient early socialisation or experiences that created negative associations.
Pain is a major contributing factor that students should never overlook. Chronic discomfort can lower tolerance and increase vigilance, making reactive behaviour far more likely. In many cases, unexpected reactivity should be treated as a clinical indicator rather than a purely behavioural one.
Environmental predictability also plays a significant role. Dogs who live in chaotic, noisy, or unpredictable environments are more likely to have unstable thresholds, leading to inconsistent behaviour.
Understanding Thresholds: A Core Skill
Thresholds determine when a dog moves from coping to not coping. A dog may comfortably observe a trigger at a distance one day but react strongly at a greater distance the next. Thresholds shift rapidly, influenced by sleep, hormones, diet, stress, weather, internal states, and handler behaviour.
For behaviour modification to work, we must learn to identify the subtle early signs of rising arousal—tension, scanning, changes in pace, increased breathing, or difficulty disengaging. Recognising these signals allows intervention before the dog reaches full reactivity. Learning only happens below threshold, and this principle forms the backbone of effective behaviour support.
Why Reactivity Is a Behaviour Issue, Not a Training Issue
Training focuses on teaching a dog what to do. Behaviour modification focuses on changing how a dog feels. These are not the same thing.
Reactive dogs are not failing to respond to cues because they are disobedient. They are unable to access trained behaviours when their nervous system is in a state of heightened arousal. This is why obedience cues do not resolve reactivity. They do not alter the dog’s underlying emotional response.
Behaviour modification tools, such as desensitisation and counterconditioning, environmental adjustments, and improved predictability, work because they address the emotional drivers of the behaviour.
Common Misunderstandings About Reactive Behaviour
One frequent misconception is that reactivity appears suddenly without warning. In reality, subtle behavioural signs appear long before the overt reaction. Another misconception is that increasing exposure will help the dog “get used to” the trigger. In most cases, this simply leads to flooding and sensitisation, making the behaviour worse. A third common oversight is failing to consider medical causes, particularly pain, which has a profound effect on tolerance and emotional stability.
Those who adopt a holistic view of behaviour—one that considers biology, environment, and learning, are far better equipped to develop effective behavioural support plans.
Final Thoughts
Reactivity is not a behavioural problem in isolation. It is the outward expression of a dog whose coping system has been overwhelmed. When we learn to understand the emotional and neurological underpinnings of reactivity, we become better observers, better analysts, and ultimately more compassionate and effective practitioners.
At DoGenius, we specialise in helping students build this critical understanding. Our courses combine scientific depth with practical application, giving future professionals the tools they need to interpret behaviour with confidence and accuracy.
