The abrupt and profound loss of smell and taste are two unique symptoms of coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus. It has been observed that about 4% of patients who recover from COVID-19 show persistent signs of a distorted sense of smell or taste 6-12 months later.

In a new study posted to the medRxiv* preprint server, scientists in the United States assessed the extent of post-COVID-19 olfactory and gustatory dysfunction to gain deeper insights into the quality and severity of the symptoms over a year.

Study: Clinical Characteristics and Long-term Symptomology of Post-COVID-19 Olfactory and Gustatory Dysfunction. Image Credit: Shchus / ShutterstockStudy: Clinical Characteristics and Long-term Symptomology of Post-COVID-19 Olfactory and Gustatory Dysfunction. Image Credit: Shchus / Shutterstock


Temporary disruptions in normal smell and taste are common in many chronic nasal inflammatory conditions and upper respiratory tract infections. However, the key distinguishing feature of COVID-19 is the sudden onset and severity of symptoms. Research has shown that up to 68% of patients report smell and taste disruptions, and about 55% recover within six months. 

An association between olfactory dysfunction and expression of the SARS-CoV2 receptor (ACE2) has been documented. However, the mechanisms underlying persistent smell and taste dysfunction remain unclear. The situation is made more complex by the fact that there is no neuronal distress or dysfunction. Some researchers have studied the mechanistic or neurological differences concerning the different SARS-CoV-2 strains, but sensory symptoms and severity in the major waves of the pandemic are yet to be analyzed.

About the Study

The main aim of the current study is to analyze the clinical characteristics of post-COVID gustatory and olfactory dysfunction. This could narrow down the predictors of persistent sensory dysfunction in patients with chronic symptomology or recovery over a year.

Adult patients with a history of COVID-19 and loss of smell or taste for more than 1 week were included in this study. A total of 426 patients enrolled in an online registry and were sent 8 study questionnaires at 4 points during a year. The questions were related to medication use, smoking history, and COVID-19 history. The terminology used for distortion of smell was dysosmia, and for distortion of taste was dysgeusia. 

Key Findings

Medical predispositions and threats, particularly nasal disease, was a key focus area of the study. This is because such conditions could make people more susceptible to sensory dysfunction after a SARS-CoV-2 infection. Chronic rhinosinusitis, nasal congestion, and environmental allergies showed significantly different frequencies across the major waves of the pandemic. However, recovery was associated only with environmental allergies, indicative of an overactive immune system capable of minimizing damage induced by COVID-19.

The participants confirmed that rinses, steroids (oral or intranasal), and nasal sprays were not able to provide temporary relief or recovery. This made it emotionally challenging and frustrating for them to cope with this condition and the slow progress. The patients also reported more significant mood disturbances, which could be due to the stigma around psychologically induced symptoms or the longevity of the symptoms.

Based on the data, the patients could fall into one of the four categories: dysosmia, dysgeusia, subjective dysosmia, and dysosmia/dysgeusia. Participants' self-reported symptoms were validated with clinical measures and compared with specific smells and tastes that could affect their daily lives. There were issues reported concerning smelling foul and dangerous odors, which is problematic for the quality and mental health. Regarding tastes, varied abilities to perceive flavors and subtle differences in food were noted.

Concluding Remarks

Lack of gender and racial/ethnical diversity was a fundamental limitation of the study, although the registry was provided in English and Spanish. It could be helpful to study the differences among patients infected at different time points within the pandemic. Future research could delve into this issue by comparing mechanistic data on post-COVID olfactory and gustatory dysfunction and clinical characteristics. 

Overall, COVID-19 is characterized by persistent gustatory and olfactory dysfunction, which occurs in conjunction with acute symptoms of infection but is not ameliorated by them. This study helped gain insights into the quality and severity of smell and taste dysfunction patients still experience post-infection. Despite being a self-reported data-driven study and unable to measure the smell and taste abilities of all participants, researchers noted a marked similarity among the recruited participants. 

The next goal would be to understand the mechanism underlying these clinical features in the current study and compare them with the registry data. This could be crucial to come up with prognosis trajectories for patients according to potential SARS-CoV-2 strain exposure and testing out novel targeted courses of treatment.

*Important Notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

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