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.