The clinical manifestations of COVID-19 can range from mild, cold-like symptoms typically associated with respiratory tract infections, such as cough and fever, to severe pneumonia with respiratory failure.
One of the common characteristics that sometimes differentiates COVID-19 from other respiratory diseases is the alteration of smell and/or taste. It mainly consists of a decrease or loss of smell (hyposmia or anosmia), and taste (hypogeusia and ageusia).
Smell and Taste Physiology
The sense of smell results from interactions between a volatile compound and the chemoreceptors expressed on the olfactory sensory neurons. These neurons are located at the top of the nasal cavity and are surrounded by supporting cells. Upon activation of these neurons, action potentials are transmitted to the olfactory bulb and amygdala, the hippocampus, and the primary olfactory cortex. Any alterations in this pathway can cause olfactory disorders.
The perception of flavors is complex and involves the senses of taste and smell as well as chemesthesis. It requires the activation of gustatory receptors on the tongue, which receive innervation from cranial nerves VII, IX and X, and recognize the five taste modalities (sweet, bitter, salty, sour, and umami). The gustatory cues are combined with the sensations provided by retronasal olfaction to give rise to flavors, and finally, chemesthesis contributes to the perception of certain characteristics, such as spiciness or cold.
COVID-19 patients usually report a loss of taste or smell without nasal congestion or discharge, which could be the consequence of a localized impairment of airflow conduction or sensorineural damage.
New Study Results
In a new study published in the journal JAMA Otolaryngology-Head & Neck Surgery, researchers have found that around one-third of people who report taste loss after COVID-19 may have genuinely lost some of their basic sense of taste.
The study led by researchers from the University of Trieste in Italy wanted to discover the proportion of people who say they have trouble with basic taste sensation after COVID-19 have possible damage to their taste buds.
The study included a total of 105 patients at the University’s ear, nose, and throat clinic who reported a disruption of their ability to taste sweet, sour, salty, or bitter for more than 3 months after a SARS-CoV-2 infection.
They used different tests, including a Sniffin’ Sticks test of olfaction and a Taste Strips test of basic taste perceptions, and found that the Taste Strips test confirmed hypogeusia (loss of basic tastes) in around 42% of the patients.
After adjusting the possible contribution of age with loss of some ability to discriminate basic tastes, 29% of the patients still appeared to have hypogeusia as a result of COVID-19.
“The mechanism is unclear but could involve direct damage to the taste buds, reduction of saliva production (a dry nose and mouth is commonly reported after [COVID-19]), or a more central process (although this is less likely),” said Prof. Hopkins, a professor of rhinology at Guy’s Hospital, London, UK, and one of the authors of the study.
Taste bud cells carry the ACE2 receptor in their membrane, which the virus uses to infect cells. But inflammation or increased blood clotting as a result of the infection, for example, could also indirectly harm the cells.
Mastrangelo A, Bonato M, Cinque P. Smell and taste disorders in COVID-19: From pathogenesis to clinical features and outcomes. Neurosci Lett. 2021;748:135694. doi:10.1016/j.neulet.2021.135694
Boscolo-Rizzo P, Hummel T, Hopkins C, et al. Comprehensive Chemosensory Psychophysical Evaluation of Self-reported Gustatory Dysfunction in Patients With Long-term COVID-19: A Cross-sectional Study. JAMA Otolaryngol Head Neck Surg. Published online January 06, 2022. doi:10.1001/jamaoto.2021.3993
James Kingsland (2022, Jan 11). Loss of basic taste after COVID-19 more common than thought. Medical News Today. Retrieved from: