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Objective/Hypothesis With the COVID‐19 pandemic, chemosensory dysfunction are among the most prevalent symptoms. Most reports are subjective evaluations, which have been suggested to be unreliable. The objective is to test chemosensory dysfunction and recovery based on extensive psychophysical tests in COVID‐19 during the course of the disease. Study Design Prospective cohort study. Methods A total of 111 patients from four centers participated in the study. All tested positive for SARS‐COV‐2 with RT‐PCR. They were tested within 3 days of diagnosis and 28 to 169 days after infection. Testing included extensive olfactory testing with the Sniffin' Sticks test for threshold, discrimination and identification abilities, and with the Taste Sprays and Taste Strips for gustatory function for quasi‐threshold and taste identification abilities. Results There was a significant difference in olfactory function during and after infection. During infection 21% were anosmic, 49% hyposmic, and 30% normosmic. After infection only 1% were anosmic, 26% hyposmic, and 73% normosmic. For gustatory function, there was a difference for all taste qualities, but significantly in sour, bitter, and total score. Twenty‐six percent had gustatory dysfunction during infection and 6.5% had gustatory dysfunction after infection. Combining all tests 22% had combined olfactory and gustatory dysfunction during infection. After infection no patients had combined dysfunction. Conclusions Chemosensory dysfunction is very common in COVID‐19, either as isolated smell or taste dysfunction or a combined dysfunction. Most people regain their chemosensory function within the first 28 days, but a quarter of the patients show persisting dysfunction, which should be referred to specialist smell and taste clinics for rehabilitation of chemosensory function. Level of Evidence 3 Laryngoscope, 131:1095–1100, 2021

Abstract:In the last years, an increasing interest has been paid to the olfactory system, particularly to its abilities of plasticity and its potential continuous neurogenesis throughout adult life. Although mechanisms underlying adult neurogenesis have been largely investigated in animals, to some degree they remain unclear in humans. Based on human research findings, the present review will focus on the olfactory bulb as an evidence of the astonishing plasticity of the human olfactory system.