ageusia

Ageusia is the complete loss of taste perception, resulting in an inability to detect the basic taste modalities—sweet, sour, salty, bitter, and umami—on the tongue and surrounding oral mucosa. It is distinct from hypogeusia (reduced taste) and dysgeusia (distorted or unpleasant taste). Taste relies on gustatory receptors in taste buds innervated by the chorda tympani branch of the facial nerve (VII), the glossopharyngeal nerve (IX), and, to a lesser extent, the vagus nerve (X), with central processing in the gustatory cortex. Loss of taste can be peripheral, due to damage to taste buds or nerves, or central, from brain injury or neurodegenerative disease, and may be transient or permanent.

Common causes include post-viral infections (including SARS-CoV-2), head and neck radiation or chemotherapy, certain medications, and nutritional deficiencies (notably zinc and B vitamins). Other etiologies encompass autoimmune neuropathies, diabetes-related neuropathy, traumatic injury to gustatory nerves, nasal or sinus disease affecting odor and taste, and surgical injuries near the gustatory pathways. Olfactory dysfunction often accompanies or mimics taste loss, since smell contributes substantially to flavor perception.

Diagnosis relies on clinical history and examination, supplemented by objective taste testing (taste strips or solutions) and olfactory testing. Laboratory workup may assess zinc, B12, and other nutritional factors; imaging or neurologic evaluation is pursued if focal deficits or persistent symptoms exist.

Management targets the underlying cause when possible, with nutritional supplementation for deficiencies, supportive care, and, in some cases, olfactory training. Prognosis varies by cause, with many cases improving over weeks to months, while others may be permanent after nerve injury.