The Importance of Considering Olfactory Dysfunction During the COVID-19 Pandemic and in Clinical Practice

The emergence of a worldwide pandemic due to coronavirus disease 2019 (COVID-19) and frequent reports of smell loss in COVID-19-infected patients have brought new attention to this very important sense. Data are emerging that smell impairment is a prominent symptom in COVID-19 and that this coronavirus behaves differently in causing olfactory dysfunction compared with other respiratory viruses. Anosmia and hyposmia, the complete and partial loss of smell, respectively, can result from many causes, most commonly from viral infections, sinonasal disease, and head trauma. Olfactory dysfunction negatively impacts quality of life, because sense of smell is important for flavor perception and the enjoyment of food. Olfaction is also important for the detection of warning smells, such as smoke, natural gas leaks, and spoiled food. Allergists and immunologists frequently encounter anosmia and hyposmia in patients with severe chronic rhinosinusitis with nasal polyps, and will likely see more infection-induced olfactory dysfunction in the era of COVID-19. Therefore, now more than ever, it is crucial that we understand this impairment, how to evaluate and how to measure it. In this review, we offer a clinically relevant primer for the allergist and immunologist on olfactory dysfunction subtypes, exploring the pathophysiology, appropriate clinical assessment, objective smell testing, and management of this condition. We will also focus on the emerging literature on COVID-19 olfactory dysfunction, its unique features, and its important implications for this pandemic.