Reactivity is a strong reaction demonstrated by a dog in response to a relatively mild trigger. This trigger can be another dog, a person, a specific object, or a sudden change in the environment. Each dog's reactive behavior will look different, however it usually involves some element of barking, growling, or lunging towards the trigger, and occurs on a regular and somewhat predictable basis.
Reactivity cannot be determined based on a single event, nor is it based on a dog's reaction to an overwhelming event or item. Barking, growling, and lunging are normal behaviors, and should be expected in response to truly intense situations.
Reactivity is typically the result of anxiety or fear, although some dogs will behave in a reactive manner for other reasons; frustration or over-excitement often results in a dog that cannot control itself. This is often seen when on leash or behind fences or other barriers.
Reactivity should not be confused with aggression because the reactive dog is not intending to cause harm. It is generally assumed that the reactive dog is “all bark and no bite,” and that his behavior is used to scare away whatever is worrying him or causing him concern. Despite this, one should use care when working with a reactive dog as the heightened arousal and out-of-control nature of his behavior increases the risk accidental harm.
Reactivity can be reduced, and many reactive dogs will improve with the use of a well-developed, well-implemented behavior modification program. If you think your dog might be reactive, I encourage you to consult with a trainer experienced in working with behavior problems.