Taste: Disorders

Taste disorders are broadly classified as losses (i.e., ageusia and hypogeusia) or as distortions of gustatory function (i.e., dysgeusia). Ageusia is the complete absence of the ability to detect or recognize any taste quality, including sweet, sour, salty, bitter, as well as less familiar taste sensations, including umami (meatlike taste of glutamate salts), fatty, metallic, starchy/polysaccharide, chalky, and astringent. Hypogeusia is the reduced ability to detect or recognize taste stimuli and refers both to generalized loss of sensitivity across [Page 958]all taste qualities or to decrements that are limited to a specific taste quality, such as salty or bitter. A person with hypogeusia requires more molecules (or ions) for a taste sensation to be perceived and recognized compared to a person with normal taste perception.

Dysgeusia may or may not be correlated with loss of sensitivity and can occur in the presence or absence of a stimulus. To a person with dysgeusia, the presence of foods or beverages in the mouth that are normally pleasant may taste unpleasant or induce an inappropriate taste sensation, such as metallic. Furthermore, the time course of taste sensations may be altered, resulting in taste perse-veration (prolonged persistence) or rapid extinction. Abnormal taste sensations may even occur when food and beverages are not present in the oral cavity. Loss or diminution of sensitivity for a single taste quality, such as salty, can distort the overall taste of a mixture resulting in dysgeusia. Most patients with taste disorders exhibit hypogeusia or dysgeusia; ageusia is rare. People with smell disorders often mistake their symptoms for a taste disorder. This confusion arises because odor sensations typically occur simultaneously with taste signals during mastication of food. Odorous molecules released from food in the oral cavity are transported to smell receptors up the back of the throat to the nasal cavity (called retronasal olfaction). Reductions in odor sensations via retronasal olfaction simply reduce the odorous component of the flavor of food but not the gustatory (taste) component. This entry describes the occurrences and causes of taste disorders, as well as burning mouth syndrome and recovery and treatment of taste disorders.