Taste and Smell Disorders
Our senses of taste and smell give us great pleasure. Taste helps us enjoy food and beverages. Smell lets us enjoy the scents and fragrances like roses or coffee. Taste and smell also protect us, letting us know when food has gone bad or when there is a gas leak. They make us want to eat, ensuring we get the nutrition we need.
People with taste disorders may taste things that aren't there, may not be able to tell the difference in tastes or can't taste at all. People with smell disorders may lose their sense of smell, or things may smell different. A smell they once enjoyed may now smell bad to them.
Many illnesses and injuries can cause taste and smell disorders, including colds and head injuries. Some drugs can also affect taste and smell. Most people lose some ability to taste and smell as they get older. Treatment varies, depending on the problem and its cause.
Every year, thousands of people develop problems with their sense of smell. If you experience a problem with your sense of smell, call your doctor.
Many people who have smell disorders also notice problems with their sense of taste. If you would like more information about your sense of taste, the fact sheet Taste Disorders may answer some of your questions.
How does our sense of smell work?
The sense of smell is part of our chemical sensing system, or the chemosenses. Sensory cells in our nose, mouth, and throat have a role in helping us interpret smells, as well as taste flavors. Microscopic molecules released by the substances around us (foods, flowers, etc.) stimulate these sensory cells. Once the cells detect the molecules they send messages to our brains, where we identify the smell.
Olfactory, or smell nerve cells, are stimulated by the odors around us--the fragrance of a gardenia or the smell of bread baking. These nerve cells are found in a small patch of tissue high inside the nose, and they connect directly to the brain. Our sense of smell is also influenced by something called the common chemical sense. This sense involves nerve endings in our eyes, nose, mouth, and throat, especially those on moist surfaces. Beyond smell and taste, these nerve endings help us sense the feelings stimulated by different substances, such as the eye-watering potency of an onion or the refreshing cool of peppermint.
It's a surprise to many people to learn that flavors are recognized mainly through the sense of smell. Along with texture, temperature, and the sensations from the common chemical sense, the perception of flavor comes from a combination of odors and taste. Without the olfactory cells, familiar flavors like coffee or oranges would be harder to distinguish.
What are the smell disorders?
People who experience smell disorders experience either a loss in their ability to smell or changes in the way they perceive odors. As for loss of the sense of smell, some people have hyposmia, which is when their ability to detect odor is reduced. Other people can't detect odor at all, which is called anosmia. As for changes in the perception of odors, some people notice that familiar odors become distorted. Or, an odor that usually smells pleasant instead smells foul. Still other people may perceive a smell that isn't present at all.
Causes of smell disorders
Smell disorders have many causes, some clearer than others. Most people who develop a smell disorder have recently experienced an illness or an injury. Common triggers are upper respiratory infections and head injuries.
Among other causes of smell disorders are polyps in the nasal cavities, sinus infections, hormonal disturbances, or dental problems. Exposure to certain chemicals, such as insecticides and solvents, and some medicines have also been associated with smell disorders. People with head and neck cancers who receive radiation treatment are also among those who experience problems with their sense of smell.
Doctors and scientists have developed tests to determine the extent and nature of a person's smell disorder. Tests are designed to measure the smallest amount of odor patients can detect as well as their accuracy in identifying different smells. In fact, an easily administered "scratch and sniff" test allows a person to scratch pieces of paper treated to release different odors, sniff them, and try to identify each odor from a list of possibilities. In this way, doctors can easily determine whether patients have hyposmia, anosmia, or another kind of smell disorder.
Are smell disorders serious?
Yes. Like all of our senses, our sense of smell plays an important part in our lives. The sense of smell often serves as a first warning signal, alerting us to the smoke of a fire or the odor of a natural gas leak and dangerous fumes. Perhaps more important is that our chemosenses are sometimes a signal of serious health problems. Obesity, diabetes, hypertension, malnutrition, Parkinson's disease, Alzheimer's disease, multiple sclerosis, and Korsakoff's psychosis are all accompanied or signaled by chemosensory problems like smell disorders.
Is there any Treatment?
Yes. Some people experience relief from smell disorders. Since certain medications can cause a problem, adjusting or changing that medicine may ease its effect on the sense of smell. Others recover their ability to smell when the illness causing their olfactory problem resolves. For patients with nasal obstructions such as polyps, surgery can remove the obstructions and restore airflow. Not infrequently, people enjoy a spontaneous recovery because olfactory neurons may regenerate following damage.
Self care for smell disorders
The best thing you can do is see a doctor. Proper diagnosis by a trained professional, such as an otolaryngologist, is important. These physicians specialize in disorders of the head and neck, especially those related to the ear, nose, and throat. Diagnosis may lead to an effective treatment of the underlying cause of your smell disorder. Many types of smell disorders are curable, and for those that are not, counseling is available to help patients cope.
If you experience a taste problem, it is important to remember that you are not alone. Many people who have taste disorders also notice problems with their sense of smell. If you would like more information about your sense of smell, the fact sheet Smell Disorders may answer some of your questions.
How does our sense of taste work?
Taste belongs to our chemical sensing system, or the chemosenses. The complex process of tasting begins when tiny molecules released by the substances around us stimulate special cells in the nose, mouth, or throat. These special sensory cells transmit messages through nerves to the brain, where specific tastes are identified.
Gustatory or taste cells react to food and beverages. These surface cells in the mouth send taste information to their nerve fibers. The taste cells are clustered in the taste buds of the mouth, tongue, and throat. Many of the small bumps that can be seen on the tongue contain taste buds.
Another chemosensory mechanism, called the common chemical sense, contributes to appreciation of food flavor. In this system, thousands of nerve endings--especially on the moist surfaces of the eyes, nose, mouth, and throat--give rise to sensations like the sting of ammonia, the coolness of menthol, and the irritation of chili peppers.
We can commonly identify at least five different taste sensations: sweet, sour, bitter, salty, and umami (the taste elicited by glutamate, which is found in chicken broth, meat extracts, and some cheeses). In the mouth, these tastes, along with texture, temperature, and the sensations from the common chemical sense, combine with odors to produce a perception of flavor. It is flavor that lets us know whether we are eating a pear or an apple. Some people are surprised to learn that flavors are recognized mainly 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. That is because the distinguishing characteristic of chocolate, for example, what differentiates it from caramel, is sensed largely by its odor.
The most common true taste complaint is phantom taste perceptions. Additionally, testing may demonstrate a reduced ability to taste sweet, sour, bitter, salty, and umami, which is called hypogeusia. Some people can detect no tastes, called ageusia. 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.
Causes of taste disorders
Some people are born with chemosensory disorders, but most develop them after an injury or illness. Upper respiratory infections are blamed for some chemosensory losses, and injury to the head can also cause taste problems.
Loss of taste can also be caused by exposure to certain chemicals such as insecticides and by some medicines. Taste disorders may result from oral health problems and some surgeries (e.g. third molar extraction and middle ear surgery). Many patients who receive radiation therapy for cancers of the head and neck develop chemosensory disorders.
Diagnosis of taste disorders
The extent of a chemosensory disorder can be determined by measuring the lowest concentration of a chemical that a person can detect or recognize. A patient may also be asked to compare the tastes of different chemicals or to note how the intensity of a taste grows when a chemical's concentration is increased.
Scientists have developed taste testing in which the patient responds to different chemical concentrations. This may involve a simple "sip, spit, and rinse" test, or chemicals may be applied directly to specific areas of the tongue.
Are taste disorders serious?
Yes. A person with a taste disorder is challenged not only by quality-of-life issues, but also deprived of an early warning system that most of us take for granted. Taste helps us detect spoiled food or beverages and, for some, the presence of food to which we're allergic. Perhaps more serious, loss of the sense of taste can also lead to depression and a reduced desire to eat.
Abnormalities in chemosensory function may accompany and even signal the existence of several diseases or unhealthy conditions, including obesity, diabetes, hypertension, malnutrition, and some degenerative diseases of the nervous system such as Parkinson's disease, Alzheimer's disease, and Korsakoff's psychosis.
Can taste disorders be treated?
Yes. If a certain medication is the cause of a taste disorder, stopping or changing the medicine may help eliminate the problem. Some patients, notably those with respiratory infections or allergies, regain their sense of taste when the illness resolves. Often the correction of a general medical problem can also correct the loss of taste. Occasionally, recovery of the chemosenses occurs spontaneously.
Self care for taste disorders
Proper diagnosis by a trained professional, such as an otolaryngologist, is important. These physicians specialize in disorders of the head and neck, especially those related to the ear, nose, and throat. Diagnosis may lead to treatment of the underlying cause of the disorder. Many types of taste disorders are curable, and for those that are not, counseling is available to help patients cope.