Reactivity 

“Reactivity is hard on dogs- without support your dog could become aggressive.  Reactive dogs become overly aroused by common stimuli.  They may lunge, bark and growl, becoming so preoccupied with whatever is triggering the emotion that they can be difficult to control and move out of the situation.”

“Aggressive dogs show similar signs but are determined to cause harm and destruction. Any reactive dog can be pushed into aggression, which is why a reactive dog needs to be taken seriously.”

Source: “Managing Reactive Behavior.” Cornell Richard P. Riney Canine Health Center, https://www.vet.cornell.edu/departments-centers-and-institutes/riney-canine-health-center/health-info/managing-reactive-behavior