Living with a reactive dog can be difficult and for some, upsetting. When most people think of reactivity, they are immediately drawn to aggression.
Reactivity is beyond the scope of just aggression as it is really about how any species responds to stimuli. For example, you may have a dog that is very quiet normally, except when a cat is present. In this example, the focus is now on predatory drive rather than that of fear based aggression.
Many forms of reactivity are associated with frustration and sometimes the end result is different than initially believed.
A reactive dog draws a lot of attention to itself and the owner which is where the emotions come into play. They are more than likely to be avoided and excluded from social play. Many times this is the best outcome as these dogs can be aggressive.
In any event, if you are living with a reactive dog, you should be seeking advise from a creditable behaviour expert.
Their assessment and advise can often correct the behavioural pathway and improve the relationship between you and the dog.
Glenn Cooke can help you with reactivity and aggression at Canine Evolution
Pat Stuart will get you on the right path at Operant canine
This always gets a run on the show