Taste and Smell Disorders

Mechanics of Taste and Smell

Taste cells (buds) located on the tongue and soft palate release chemosensory molecules that transmit messages to higher neural centers where specific taste identification is conducted. It is thought that humans can generally discern taste sensations of sweet, salty, sour, and bitter. As Anholt explains, “the sense of smell depends on olfactory chemoreceptors high in the nasal cavity along the upper septum and cribiform plate which underlies the anterior cranial fossa.”

Odorant molecules that pass into the nose dissolve into the nasal mucosa and activate these olfactory chemoreceptors to trigger a sense of smell. Barker identifies, “There is also a chemosensory sense mediated by the trigeminal nerve (fifth cranial nerve), which is triggered by pungent and irritant compounds, such as hot peppers, horseradish, and so on, and perceived as burning or irritating. This pathway is independent from the other modalities of taste and smell.”

Disorders

A reduced ability to taste or discriminate between various tastes is called hypoguesia. In people who can detect no tastes, the condition is called aguesia. People who have a decreased ability to detect odor are said to have hyposmia. Those who cannot detect odor at all have anosmia. According to the National Institutes of Health, “true taste loss is rare; perceived loss usually reflects a smell loss, which is often confused with a taste loss. In other disorders of the chemical senses, the system may misread and or distort an odor, a taste, or a flavor. Or a person may detect a foul taste from a substance that is normally pleasant tasting. People who experience smell disorders experience either a loss in their ability to smell or changes in the way they perceive odors.”

Issues regarding quality of life may develop as patients may be unable to enjoy the taste or smell of their once-favorite foods.

Causes

Like other human senses, our sense of smell and taste can be greatly affected simply by aging. In fact, scientists have found that the sense of smell begins to decline after age 60. Aside from age, anatomic blockage is one of the most common causes of smell dysfunction. Blockage can occur secondary to the existence of disorders of the nasal septum, polyps, or nasopharyngeal tumors. As Tierney explains, “Transient olfactory dysfunction often accompanies the common cold, nasal allergies, and perennial rhinitis. About 20 percent of olfactory dysfunction is idiopathic, although it often follows a viral illness.” Ackerman has [Page 1646]identified a number of commonly used prescribed medications that can impair the sense of smell including beta-blockers, the antibiotic Ciprofloxacin, and the antimetabolite Methotrexate.

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