A NEW study has provided important insights into the biological basis of persistent taste dysfunction in patients with long COVID, suggesting that subtle molecular changes, rather than structural damage, may underlie ongoing symptoms.
Loss or alteration of taste is a well-recognised symptom of acute COVID-19, typically resolving within weeks. However, for some individuals, these disturbances persist for months or even years as part of post-acute COVID-19 syndrome. To better understand this phenomenon, researchers examined 28 non-hospitalised individuals who continued to report taste dysfunction more than 12 months after SARS-CoV-2 infection.
Objective taste testing using the Waterless Empirical Taste Test revealed that while most participants had overall taste scores within normal ranges, dysfunction was still evident. Only three individuals fell below the 10th percentile for overall taste ability, yet 11 participants experienced complete loss of at least one specific taste quality.
Sweet, Bitter, and Umami Tastes Most Affected
Notably, the study found that taste loss most commonly affected sweet, bitter, and umami sensations, while salty and sour tastes were largely preserved. These affected taste modalities share a common signalling pathway dependent on the protein PLCβ2, suggesting a targeted mechanism of dysfunction.
To investigate this further, researchers performed biopsies of fungiform taste papillae in a subset of participants. Histological analysis showed that the overall structure and nerve supply of taste buds were largely intact, with only minor abnormalities observed. Importantly, no viral RNA was detected in tissue samples, indicating that persistent symptoms are unlikely to be caused by ongoing viral presence.
Reduced Expression of Key Taste Signalling Genes Identified
Instead, molecular analysis revealed reduced expression of key genes, including PLCβ2 and TAS1R3, in taste receptor cells. These proteins are critical for signal transduction in type II taste cells, which detect sweet, bitter, and umami flavours. Their reduced expression may impair the transmission of taste signals to the brain, even when the physical structure of taste buds appears normal.
The findings suggest that long-term taste dysfunction in COVID-19 is relatively uncommon but measurable and may result from lasting molecular alterations rather than irreversible tissue damage.
Although the study was limited by its small sample size and lack of pre-infection baseline data, it provides some of the first direct evidence linking subjective taste disturbances to quantifiable biological changes. The authors emphasise the need for further research to determine whether these molecular deficits are reversible and to explore potential therapeutic strategies.
Overall, the study advances understanding of long COVID and highlights the complex, lingering effects of SARS-CoV-2 on sensory function.
Reference
Morad H et al. Taste dysfunction in long COVID. Chem Senses. 2026;51:bjaf068.
Featured image: ZAY WIN HTAI on Adobe Stock
