Ageusia is the loss of taste functions of the tongue or the absence or impairment of the sense of taste. People who can taste sweet, sour, bitter, or salty substances but have a reduced ability to do so are said to have hypogeusia. Some people are born with taste disorders. Other causes include upper respiratory and middle ear infections, radiation therapy for cancers of the head and neck, exposure to certain chemicals, some antibiotics and antihistamines, head injury, surgery to the ear, nose, and throat, poor oral hygiene, and dental problems.