Reactivity in dogs describes an over-the-top response to everyday triggers such as other dogs, people, bikes or sudden noises. Rather than a measured reaction, reactive dogs bark intensely, lunge, pull or fixate, becoming so emotionally overwhelmed they struggle to calm down or refocus. The response is fuelled by fear, frustration or over-arousal rather than intent to cause harm.
quick summary
Reactivity means a dog responds faster and more intensely than the situation warrants.
Common triggers include other dogs, strangers, moving objects like bikes, and confinement/feeling trapped on a lead
Usually driven by fear, frustration or excitement, not aggression
Barking, lunging, pulling and fixating are typical signs
Can worsen over time without intervention, and may escalate to aggression if mismanaged
What is actually going on?
Reactivity happens when a dog's emotional response overshoots the 'trigger'. Imagine seeing another dog across the street and your dog explodes into barking, pulling and lunging, unable to settle even with treats or commands. That intensity, which is completely disproportionate to the event going on in real life, is reactivity.
The root is usually fear. A dog on a lead knows they can't run away or escape from the situation (they feel trapped), so they try to look intimidating instead, barking and lunging to make the scary thing leave: if you've got a reactive dog you'll know from experience this behaviour does its job! The other dog or person moves away, the cyclist keeps rolling on by, and the reactive dog learns the behaviour is effective. This reinforcement loop is why reactivity tends to worsen without structured help.
Frustration also plays a role. Some dogs react because they desperately want to interact but cannot, creating a build-up of emotional tension that spills out as over-the-top behaviour. Excitement can look similar, with high arousal flooding the dog's ability to calm themselves down.
The key difference from aggression is intent. Reactive dogs are emotionally flooded, not strategically or intending to be harmful, even if it looks very similar. However, if a reactive dog's warning signals are repeatedly ignored or punished, reactivity can tip into defensive aggression. Research shows that reactivity is linked to impaired self-control, poor early socialisation, genetic predisposition and individual brain chemistry. Understanding what drives your dog's reactivity is the first step toward managing it effectively.
things to look out for
Explosive barking, lunging or pulling when seeing other dogs, people or moving objects
Intense fixation on the trigger, unable to disengage or respond to your voice
Hackles raised, stiff body posture, whale eye or excessive panting
Behaviour worsens with repeated exposure rather than improving naturally
Reactions triggered by specific contexts such as being on a lead, behind a fence or in crowded spaces
Inability to calm themselves down quickly after the trigger has passed
