Ageusia (from negative prefix a- and Ancient Greek γεῦσις geûsis 'taste') is the loss of taste functions of the tongue, particularly the inability to detect sweetness, sourness, bitterness, saltiness, and umami (meaning 'savory taste'). It is sometimes confused with anosmia – a loss of the sense of smell. True ageusia is relatively rare compared to hypogeusia – a partial loss of taste – and dysgeusia – a distortion or alteration of taste.

Even though ageusia is considered relatively rare it can impact individuals of any age or demographic. There has been an increase in reported cases of ageusia, due to the COVID-19 pandemic making ageusia more commonly diagnosed than before.

The complete loss of taste.

Ageusia can arise from various factors:

Ageusia resulting from a significant head injury is relatively uncommon, affecting only around 1% of individuals with this type of injury.

Ageusia can be an indication of a COVID-19 infection. Ageusia and anosmia are among the prominent symptoms commonly associated with COVID-19, with symptoms that could last up to 4 weeks. However, it is noteworthy that ageusia may manifest differently from anosmia, as anosmia primarily affects the olfactory system versus ageusia primarily affecting the gustatory receptors. As a result, emerging research indicates that the various variants of COVID-19 might be associated with differences in the severity of ageusia experienced by patients, as well as the severity of other taste and smell disorders. Implying that certain strains of the virus may have differing impacts on the sensory functions of affected individuals.

Studies investigating the prevalence of taste disorders stemming from the COVID-19 pandemic indicate that a wide range of individuals were impacted, with some experiencing these issues more severely than others:

Patients with ageusia observed in 28.0% of patients, hypogeusia in about 33.5%, and dysgeusia in about 41.3% of patients.