Scientists Finally Know Why Some People Still Can’t Taste Anything Years After Having COVID

When COVID-19 began spreading across the world, one of its most unusual symptoms quickly came into focus: the sudden disappearance of taste. People described coffee tasting like hot water or their favorite meals becoming strangely bland.

For most patients, the loss faded within weeks or months. But for a smaller group, taste never fully returned. Even years after infection, certain flavors remain muted or completely absent.

Now, a new study published in Chemical Senses provides some of the clearest biological clues yet explaining why that may happen. By examining taste tests and biopsies from people with long-lasting taste problems after COVID-19, researchers identified molecular and structural changes inside taste buds that may weaken the signals responsible for detecting flavor.

Molecular Changes in Taste Cells

Scientists from the United States and Sweden recruited 28 adults who reported altered taste more than a year after COVID-19 infection. None had been hospitalized, but all said their sense of taste changed after the illness.

The participants first completed the Waterless Empirical Taste Test, a diagnostic tool that measures the ability to recognize the five basic taste qualities—sweet, salty, sour, bitter, and umami—using flavored strips placed on the tongue.

The tests revealed a clear pattern.

Eight participants showed clearly abnormal taste scores. In addition, eleven reported losing specific tastes—most commonly sweet, bitter, and umami—while salty and sour sensations were largely preserved.

To understand what might be happening inside taste tissue, researchers took tiny biopsies from fungiform papillae, small structures on the tongue that contain clusters of taste buds. These samples allowed scientists to examine both the structure of taste buds and the molecular signals inside their cells.

In many biopsies, the team discovered reduced levels of messenger RNA that produces a protein called PLCβ2. This protein plays a key role in transmitting taste signals from receptor cells to the brain.

“PLCβ2 acts like a molecular amplifier inside taste cells,” said study co-author Thomas Finger. “It strengthens the signal before it’s transmitted to the brain. When levels are reduced, the taste signal weakens.”

The result is similar to lowering the volume on a speaker: the signal is still present, but it becomes much harder for the brain to detect.

This discovery also explains the unusual pattern seen in patients. Cells that detect sweet, bitter, and umami flavors rely on PLCβ2 signaling, while salty and sour taste cells use different molecular pathways. As a result, those latter tastes often remain intact.

A Disrupted Taste System

The scientists went further and also examined the microscopic structure of the taste buds themselves.

In many participants, taste buds appeared normal. But in others, the tissue showed subtle abnormalities, including disorganized taste bud structures or unusual taste cells located outside their typical arrangement.

These findings suggest that long-term taste loss may involve a combination of problems: weakened molecular signaling inside taste cells and structural disruptions in the taste bud tissue.

However, when the researchers tested the biopsied tissue for viral genetic material, they found no trace of SARS-CoV-2.

That means the virus itself is not lingering in the taste buds. Instead, the damage appears to persist even after the infection has cleared.

Scientists suspect that the virus may initially infect certain taste receptor cells or surrounding tissues, triggering inflammation, immune responses, or cellular stress that disrupts the signaling pathways required for normal taste.

Another possible factor involves the nerves that connect taste buds to the brain. Even if taste structures appear intact, impaired nerve signaling could prevent taste information from reaching the brain properly.

But taste bud cells typically regenerate every few weeks, replacing damaged cells with new ones. In theory, this rapid turnover should allow the system to recover quickly. Yet some patients continue to experience taste loss for more than a year after infection.

Although persistent taste dysfunction appears to affect only a minority of COVID-19 survivors, its impact can be significant. Taste plays a key role in appetite, nutrition, and emotional well-being, and losing it can make eating both difficult and joyless.

By identifying specific cellular changes linked to long-term taste loss, the new study offers scientists a clearer path toward understanding—and eventually treating—one of the pandemic’s most puzzling lingering symptoms.