Reactivity — the tendency to respond with intense, exaggerated behaviour (lunging, barking, growling) to specific triggers — is one of the most common and welfare-significant behavioural problems in companion dogs. It causes distress to dogs and owners alike, and is a leading cause of dog relinquishment. Understanding reactivity as a welfare issue enables compassionate, evidence-based management.
Reactive behaviour is typically rooted in fear, frustration, or over-arousal. A dog lunging at other dogs on lead is not "dominant" or "aggressive" — it is most commonly a dog that has learned that their signal to increase distance (barking, lunging) works, or a dog that is frustrated by the physical restriction of the lead. The behaviour is the surface expression of an underlying emotional state.
Reactive dogs experience chronic or episodic fear and stress. Every reactive incident involves a cortisol spike that can take hours to clear — meaning a reactive dog on a walk in a trigger-rich environment may be in a sustained state of physiological stress. This chronic stress impairs learning, immune function, and quality of life. Management that reduces exposure to triggers above the dog's threshold significantly improves welfare.
Punishment (leash corrections, spray bottles, shouting) for reactive behaviour increases fear and worsens reactivity over time. It may suppress the visible behaviour while increasing the underlying emotional distress — creating dogs that bite without warning. Evidence-based training never uses aversive methods for fear-based reactivity.