Ageusia is the inability to taste. True ageusia is quite rare, and it can be caused by a number of things. More commonly, people have what is known as a “taste disorder,” meaning that their sense of taste is impaired, but not entirely absent. Many taste disorders are linked to smell disorders since the experiences of smell and taste are very closely related. People who suffer from ageusia often seek medical attention, since taste is viewed as a critical sense by many humans.
In true ageusia, a patient cannot taste anything applied to his or her tongue. More commonly, people have hypogeusia, a taste disorder in which the patient has trouble differentiating tastes or experiencing certain tastes. Older people, for example, tend to be less sensitive to bitter flavors. People can also develop dysgeusia, in which the sense of taste is distorted or altered.
On its own, ageusia is a problem for many sufferers because it interferes with the enjoyment of food. Someone with ageusia may eat substantially less than he or she should, potentially experiencing malnourishment. The sense of taste is also critically important in detecting signs that food has gone “off,” in combination with the sense of smell, which means that someone with ageusia may eat something which makes him or her sick.