After a COVID-19 infection, some people take months, or even longer, to recover their sense of taste. To understand this persistent phenomenon, a recent study directly examined the taste buds of patients, providing concrete answers.
This research, published in
Chemical Senses, looked at 28 people who reported taste alterations more than a year after contracting COVID-19, without having been hospitalized. Among them, nearly one-third had abnormal scores on taste tests, with notable loss for sweet, bitter, and umami flavors, while salty and sour were generally preserved. To understand these persistent symptoms, samples of taste buds were analyzed.
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The scientists discovered that certain taste receptor cells contained less messenger RNA needed to produce a protein called PLCβ2. This protein plays an essential role in amplifying signals for sweet, bitter, and umami tastes before they are transmitted to the brain. Its reduction could weaken these signals, explaining why these tastes are particularly affected. In contrast, the detection mechanisms for salty and sour function differently and do not depend on this protein.
Beyond these molecular aspects, microscopic observation showed structural changes in the taste buds of some participants. While several had tissues of normal appearance, others exhibited visible disorganization. These architectural changes, combined with molecular disruptions, could together contribute to prolonged taste dysfunctions after infection.
Normally, taste bud cells renew themselves every two to four weeks. However, the study indicates that alterations in signaling pathways can persist much longer in some people. The authors note that further research is needed to determine whether these changes are reversible and if treatments could help restore normal taste signaling.
The renewal of taste cells
The taste buds on our tongue are composed of cells that do not live very long. They renew themselves regularly, approximately every two to four weeks, from stem cells located at their base. This constant process helps maintain a fresh and functional perception of flavors, even after minor damage caused by hot food or temporary infections.
When this renewal is disrupted, for example by a viral infection like COVID-19, the new cells may not form correctly or may present defects. This can lead to a lasting alteration of taste, as damaged cells are not replaced effectively. The virus could affect the signals that regulate this regeneration, leading to less functional taste buds.
This study shows that even after the virus has cleared, some individuals retain abnormalities in their taste cells. This points to the fact that COVID-19 could leave lasting marks on cellular mechanisms, beyond the simple acute infection. Understanding how the virus interferes with this renewal could help develop approaches to stimulate taste recovery in affected patients.