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Anosmia is complete loss of smell. Hyposmia is partial loss of smell. Most people with anosmia can recognize salty, sweet, sour, and bitter substances but cannot tell the difference between specific flavors. The ability to tell the difference between flavors actually depends on smell, not the taste receptors on the tongue. Therefore, people often complain of losing their sense of taste and of not enjoying food.
Causes
Anosmia occurs when swelling or another blockage of the nasal passages prevents odors from reaching the olfactory area or when parts of the olfactory area or its connections to the brain are destroyed (see Symptoms of Nose and Throat Disorders: Some Causes and Features of Anosmia ). The olfactory area is where odors are detected and is located high in the nose (see Symptoms of Nose and Throat Disorders: How People Sense Flavors ).
Common causes:
The most common causes include
A common cause of permanent loss of smell is a head injury, as may occur in a car accident. Head injury can damage or destroy fibers of the olfactory nerves (the pair of cranial nerves that connect smell receptors to the brain) where they pass through the roof of the nasal cavity. Sometimes the injury involves a fracture of the bone (cribriform plate) that separates the brain from the nasal cavity. Damage to the olfactory nerves can also result from infections (such as abscesses) or tumors near the cribriform plate.
Another common cause is an upper respiratory infection, especially influenza (flu). Flu may be the cause in up to one quarter of people with hyposmia or anosmia. Alzheimer's disease and some other degenerative brain disorders (such as multiple sclerosis) can damage the olfactory nerves, commonly causing loss of smell.
Less common causes:
Drugs can contribute to anosmia in susceptible people. Polyps, tumors, other infections in the nose, and seasonal allergies (allergic rhinitis) may interfere with the ability to smell. Occasionally, serious infections of the nasal sinuses or radiation therapy for cancer causes a loss of smell or taste that lasts for months or even becomes permanent. These conditions can damage or destroy smell receptors. The role of tobacco is uncertain. A very few people are born without a sense of smell.
Evaluation
The following information can help people decide whether a doctor's evaluation is needed and help them know what to expect during the evaluation.
Warning signs:
The following findings are of particular concern:
When to see a doctor:
People who have warning signs should see a doctor within a day or two. Other people should see a doctor when possible, but a doctor's evaluation is not urgent unless other symptoms develop.
What the doctor does:
Doctors first ask questions about the person's symptoms and medical history and then do a physical examination. What doctors find during the history and physical examination often suggests a cause and the tests that may need to be done (see Symptoms of Nose and Throat Disorders: Some Causes and Features of Anosmia).
Doctors ask about onset and duration of anosmia and its relation to any cold, bout of flu, or head injury. They note other symptoms such as a runny or stuffy nose and whether any nasal discharge is watery, bloody, thick, or foul-smelling. Doctors seek out any neurologic symptoms, especially those that involve a change in mental status (for example, difficulty with short-term memory) or the cranial nerves (for example, double vision or difficulty speaking or swallowing). Questions about the person's medical history involve sinus disorders, head injury or surgery, allergies, drugs used, and exposure to chemicals or fumes.
During the physical examination, doctors inspect the nasal passages for swelling, inflammation, discharge, and polyps. Doctors also do a complete neurologic examination that is particularly focused on mental status and the cranial nerves.
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Some Causes and Features of Anosmia |
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Cause
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Common Features*
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Tests
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Blockage within the nose
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Nasal allergies
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In people who have chronic allergy symptoms (such as nasal congestion and a clear discharge)
No pain
Symptoms that often occur during certain seasons or after exposure to specific substances
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A doctor's examination
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Nasal polyps
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Polyps that are usually seen during the examination
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A doctor's examination
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Destruction of smell receptors
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Chronic sinusitis
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A thick, foul-smelling nasal discharge most or all of the time
Previous sinus infections
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A doctor's examination
Usually CT
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Some viral upper respiratory infections (such as influenza)
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Loss of smell that occurs after an infection
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A doctor's examination
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Tumors (a rare cause)
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Possibly vision problems or only loss of smell
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CT
MRI
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Drugs (such as amphetamines, enalapril, estrogen, naphazoline, phenothiazines, and reserpine or use of decongestants for a long time)
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Usually in people who report taking such drugs
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A doctor's examination
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Toxins (such as cadmium and manganese)
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Usually in people who report exposure to such toxins
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A doctor's examination
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Destruction of olfactory pathways in the brain
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Alzheimer's disease
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Progressive confusion and loss of recent memory
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MRI
Sequential memory tests
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Head injuries
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In people who have had a head injury
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CT
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Degenerative neurologic disorders (such as multiple sclerosis)
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Intermittent episodes of other symptoms of nervous system dysfunction, such as weakness, numbness, or difficulty speaking, seeing, or swallowing
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MRI
Sometimes a spinal tap
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Brain surgery or infection
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In people who have had brain surgery or a brain infection
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CT or MRI
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Brain tumors
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Sometimes headache and/or symptoms of nervous system dysfunction
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CT or MRI
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*Features include symptoms and results of the doctor's examination. Features mentioned are typical but not always present.
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CT = computed tomography; MRI = magnetic resonance imaging.
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Testing:
To test smell, doctors hold common fragrant substances (such as soap, a vanilla bean, coffee, and cloves) under the person's nose, one nostril at a time. The person is then asked to identify the smell. Smell can also be tested more formally using standardized commercial smell test kits. One kit requires the person to scratch and sniff many different smell samples and try to identify them. Another kit contains diluted samples of a smelly chemical. Doctors see how dilute the sample can be before the person can no longer smell the chemical.
If there is no clear cause of anosmia, computed tomography (CT) or magnetic resonance imaging (MRI) of the head (including the sinuses) is done to look for structural abnormalities (such as a tumor, an abscess, or a fracture).
Treatment
Doctors treat the cause of the anosmia. For example, people with sinus infections and irritation may be treated with steam inhalation, nasal sprays, antibiotics, and sometimes surgery. However, the sense of smell does not always return even after successful treatment of sinusitis. Tumors are surgically removed or treated with radiation, but such treatment usually does not restore the sense of smell. Polyps in the nose are removed, sometimes restoring the ability to smell. People who smoke tobacco should stop.
There are no treatments for anosmia itself. People who retain some sense of smell may find that adding concentrated flavoring agents to food improves their enjoyment of eating. Smoke alarms, important in all homes, are even more essential for people with anosmia because they cannot smell smoke. Doctors recommend that people with anosmia use caution before consuming stored food and using natural gas for cooking or heating, because they may have difficulty detecting food spoilage or gas leaks.
Essentials for Older People
The ability to smell decreases as people age. The decrease is caused by a loss of smell receptors. People typically notice changes in smell by age 60. After age 70, changes are substantial.
Key Points
Last full review/revision July 2012 by Marvin P. Fried, MD
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