hypogeusia

Hypogeusia is a reduced ability to taste, a partial loss of the sense of taste. It is distinct from ageusia, the complete loss of taste, and from dysgeusia, a distortion or unpleasant alteration of taste. Hypogeusia can affect one or more of the basic tastes—sweet, sour, salty, bitter, and umami—or overall taste perception. Taste perception relies on gustatory receptors in taste buds, primarily on the tongue, with signals carried by the facial (CN VII), glossopharyngeal (CN IX), and vagus (CN X) nerves to the brain. Flavor is also influenced by smell, so concurrent olfactory loss can mimic or worsen hypogeusia.

Common causes include upper respiratory infections and chronic nasal or sinus disease that impair odor and taste, medications (including those known to alter taste), nutritional deficiencies such as zinc or vitamin B12 deficiency, radiation therapy to the head or neck, aging, smoking, diabetes and other metabolic disorders, head trauma, and neurologic conditions such as Parkinson’s disease or Alzheimer’s disease. Local factors such as poor oral health, dental disease, and dry mouth can contribute as well.

Evaluation typically involves a clinical history and examination of the mouth, nose, and throat, along with a review of medications. Objective gustatory testing may use standardized tastants, and olfactory testing can help distinguish true taste loss from smell impairment. Laboratory tests may include zinc level, metabolic panel, and nutritional markers; imaging or neurologic consultation is considered if central or structural causes are suspected.

Treatment focuses on the underlying cause: adjusting or stopping offending medications, treating infections or nasal disease, correcting nutritional deficiencies, improving saliva production, and addressing lifestyle factors such as smoking. Many cases improve when the underlying condition is treated, but some patients—with persistent or neuropathic etiologies—may have ongoing hypogeusia.