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Smell and Taste Disorders (Chemosensory Disorders)

The senses of smell and taste

The senses of smell and taste are chemosenses and belong in the chemical sensing system.

The processes of smelling and tasting are complex. They begin when molecules are released by substances that stimulate the sensory cells in the nose, mouth, or throat.

Olfactory nerve cells are stimulated by odors. They are found in tissue located high inside the nose, and connect directly to the brain.

Gustatory nerve cells are stimulated by the taste of food and beverage. They are located in the taste buds of the mouth and throat.

These sensory cells transmit messages to the brain through the nerves, where specific tastes and smells are identified.

Another chemosensory process, called common chemical sense, also contributes to smell and taste. These cells alert the brain to sensations, such as heat (as from peppers) or cool (as from menthol).

How do taste and smell interact?

The four basic taste sensations are sweet, sour, bitter, and salty.

When these tastes, along with texture, temperature, and information from the common chemical sense, combine with odors, the perception of flavor occurs. Flavor defines the food that is eaten, and is recognized mainly through the sense of smell.

Source: National Institute on Deafness and Other Communication Disorders

What are smell and taste disorders?

The loss of the senses of smell (anosmia) and taste (ageusia) are the most common chemosensory disorders.

The reduced ability to smell (hyposmia) or to taste sweet, sour, bitter or salty substances (hypogeusia) are also common.

In other disorders of the chemosenses, odors, tastes, or flavors may be misread or distorted, causing a person to detect an unpleasant odor or taste from something that is normally pleasant to taste or smell. These disorders are important because they can have a significant impact on quality of life and be a sign of underlying disease. 

Smell disorders are serious because they damage the early warning system that can alert a person to such things as:

  • Fire
  • Poisonous fumes
  • Leaking gas
  • Spoiled food and beverages

Abnormalities in taste and smell can accompany or indicate the existence of diseases or conditions, such as:

  • Obesity
  • Diabetes
  • Hypertension
  • Malnutrition
  • Degenerative diseases of the nervous system, such as:
    • Parkinson's disease
    • Alzheimer's disease
    • Multiple sclerosis

What causes smell and taste disorders?

Although some people are born with chemosensory disorders, most are caused by:

  • Illness (for example, upper respiratory infection, sinus infection, and allergies)
  • Injury to the head
  • Hormonal disturbances
  • Dental, oral, or perioral problems
  • Nasal polyps
  • Exposure to certain chemicals
  • Certain medications
  • Exposure to radiation therapy for head or neck cancer
  • Over-the-counter and prescription medications
  • Intranasal cocaine
  • Cigarette smoking

How are smell and taste disorders diagnosed?

In addition to a complete medical history and physical examination, diagnostic procedures may include:

  • Measuring the lowest concentration of a chemical that a person can recognize
  • Comparing tastes and smells of different chemicals
  • "Scratch and sniff" tests
  • "Sip, spit, and rinse" tests where chemicals are directly applied to specific areas of the tongue

Treatment for smell and taste disorders

Specific treatment for smell and taste disorders will be determined by your doctor based on:

  • Your age, overall health, and medical history
  • Extent of the disorder
  • Your tolerance for specific medications, procedures, or therapies
  • Expectations for the course of the disorder
  • Your opinion or preference

Treatment may include:

  • Stopping or changing medications that contribute to the disorder
  • Correction of the medical problem that is causing the disorder
  • Surgical removal of obstructions that may be causing the disorder
  • Counseling
  • Smoking cessation

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