*3.3.3 United airway hypothesis/disease*

Upper and lower airways are considered a unified morphological and functional unit, and the connection existing between them has been observed for many years, both in health and in disease [35]. The respiratory system is integrated, and thus the allergic diseases of the lower (i.e., asthma) and the upper respiratory tract (allergic rhinitis) have similar pathogenesis and should be considered as one. Indeed, precious studies have shown an overlap in the clinical presentation of these two diseases where patients with allergic rhinitis are at risk for asthma.
