Review of the upper airway, including olfaction, as mediator of symptoms.

The upper airway serves as air conditioner, filter, and warning device. Two neurological modalities, olfaction and trigeminal chemoreception, inform us of the chemical qualities of the air we breathe. A number of poorly understood conditions, including nonallergic rhinitis, irritant-induced rhinitis, odor-triggered asthma, odor-triggered panic attacks, chemical-induced olfactory dysfunction, and irritant-associated vocal cord dysfunction, involve induction of symptoms by odorant and/or irritant chemicals in the upper airway. This article is a summary of the knowledge and theories about these various conditions, and highlights those aspects of nasal anatomy, physiology, and pathophysiology relevant to their understanding.