Problems with these senses have a big impact on our lives. Smell and taste contribute to our enjoyment of life by stimulating a desire to eat which not only nourishes our bodies, but also enhances our social activities. When smell and taste become impaired, we eat poorly, socialize less and feel worse. Smell and taste warn us of dangers, such as fire, poisonous fumes and spoiled food. Loss of the sense of smell may indicate sinus disease, growths in the nasal passages, or, at times, brain tumors.
Smell and taste belong to our chemical sensing system (chemosensation). The complicated process of smelling and tasting begins when molecules released by the substances around us stimulate special nerve cells in the nose, mouth and throat. These cells transmit messages to the brain, where specific smells or tastes are identified.
The fragrance from a flower or the smell of fresh bread baking stimulate the Olfactory (smell nerve) cells which are found in a tiny patch of tissue high up in the nose and are connected directly to the brain.
The Gustatory (taste nerve) cells are clustered in the taste buds of the mouth and throat. They react to food or drink mixed with saliva. Many of the small bumps that can be seen on the tongue contain taste buds. These surface cells send taste information to nearby nerve fibers, which send messages to the brain.
Our body’s ability to sense chemicals is another chemosensory mechanism that contributes to our senses of smell and taste. In this system, thousands of free nerve endings, especially on the moist surfaces of the eyes, nose, mouth and throat, identify sensations like the sting of ammonia, the coolness of menthol and the “heat” of chili peppers.
The sense of smell is most accurate between the ages of 30 and 60 years and begins to decline after age 60; a large proportion of elderly persons lose their smelling ability. Women of all ages are generally more accurate than men in identifying odors. Some people are born with a poor sense of smell or taste. Upper respiratory infections are blamed for some losses and injury to the head can also cause smell or taste problems.
Loss of the sense to smell and taste may result from polyps in the nasal or sinus cavities, hormonal disturbances or dental problems. They also can be caused by prolonged exposure to certain chemicals such as insecticides and by some medicines. Tobacco smoking is the most concentrated form of pollution that most people are exposed to and impairs the ability to identify odors and diminishes the sense of taste. Quitting smoking some times improves the function to taste and smell.
Radiation therapy patients with cancers of the head and neck often complain of lost smell and taste. These senses can also be lost in the course of some diseases of the nervous system.
It is common for patients who have lost their larynx (voice box) to complain of poor ability to smell and taste. Laryngectomy patients can use a special “bypass” tube to breathe through the nose again. The enhanced air flow through the nose helps smell and taste sensations to be re-established.
The extent of the loss of smell or taste can be tested using the lowest concentration of a chemical that a person can detect and recognize. A patient may also be asked to compare the smells or tastes of different chemicals and how the intensities of smells and tastes grow when a chemical concentration is increased.
- Smell-Scientists have developed an easily administered “scratch-and-sniff” test to evaluate the sense of smell.
- Taste-Patients react to different chemical concentrations in taste testing; this may involve a simple “sip, spit and rinse” test, or chemicals may be applied directly to specific areas of the tongue.
Sometimes certain medications are the cause of smell or taste disorders and improvement occurs when that medicine is stopped or changed. Although certain medications can cause chemosensory problems, others, particularly anti-allergy drugs, seem to improve the senses of taste and smell. Some patients, notably those with serious respiratory infections or seasonal allergies, regain their smell or taste simply by waiting for their illness to run its course. In many cases, nasal obstructions, such as polyps, can be removed to restore airflow to the receptor area and can correct the loss of smell and taste.
If you experience problems in smelling or tasting, it would be helpful for your doctor to try and write down and identify the circumstances surrounding your loss of taste or smell. When did you first become aware of it? Did you have a cold or flu? A head injury? Were you exposed to air pollutants, pollens, dander or dust to which you might be allergic? Is this a recurring problem? Does it come in any special season, like hay fever time? Bring all this information with you when you visit your physician at OOA, who deals with diseases of the nose and throat. Proper diagnosis by a trained professional can provide reassurance that your illness is not imaginary. You may even be surprised by the results. For example, what you may think is a taste problem could actually be a smell problem, because much of what you taste is really caused by smell. Diagnosis may also lead to treatment of an underlying cause for the disturbance. Remember, many types of smell and taste disorders are reversible.
Four commonly identified taste sensations: sweet * sour * bitter * salty
Certain tastes combine with texture, temperature and odor to produce a flavor that allows us to identify what we are eating. Some flavors are recognized through the sense of smell. If you hold your nose while eating chocolate, for example, you will have trouble identifying the chocolate flavor, even though you can distinguish the food’s sweetness or bitterness. This is because the familiar flavor of chocolate is sensed largely by odor. So is the well-known flavor of coffee. This is why a person who wishes to fully savor a delicious flavor will exhale through his nose after each swallow.Taste and smell cells are the only cells in the nervous system that are replaced when they become old or damaged. Scientists are examining this phenomenon while studying ways to replace other damaged nerve cells.