Bronchial hyper reactivity (BHR) is the increased response of the airway to stimuli.BHR can be present very early in life.Pulmonary functional testing can be used as a diagnostic tool, to assess response to therapy and to follow the longitudinal course of the child.There may be some genetic basis for the development of BHR but that environmental factors are more important.There is a significant familial predisposition for BHR among patients with allergic rhinitis.