Anosmia is complete loss of smell. Hyposmia is partial loss of smell. Most people with anosmia can taste 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 with anosmia often complain of losing their sense of taste and of not enjoying food.
A loss of smell receptors due to aging causes a decreased ability to smell in older people. People typically notice changes in smell by age 60. After age 70, changes are substantial.
Causes of Anosmia
Anosmia that is not the result of aging 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 table Some Causes and Features of Anosmia). The olfactory area, where odors are detected, is located high in the nose (see How People Sense Flavors).
Common causes
The most common causes include
Head injury (young adults)
Viral infections
Alzheimer disease (older adults)
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 disease and some other degenerative brain disorders (such as multiple sclerosis) can damage the olfactory nerves, commonly causing loss of smell.
Less common causes
Medications 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.
Anosmia or hyposmia may be an early symptom of COVID-19, an acute respiratory illness that can be severe. COVID-19 is caused by the coronavirus called SARS-CoV2.
Evaluation of Anosmia
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:
Recent head injury
Symptoms of nervous system dysfunction, such as weakness, trouble with balance, or difficulty seeing, speaking, or swallowing
Sudden start of symptoms
Local or global outbreak of COVID-19
When to see a doctor
People who have warning signs should see a doctor right away. Other people should see a doctor when possible.
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 table Some Causes and Features of Anosmia).
Doctors ask when and how anosmia started and how long it has lasted. They also ask whether it started before or shortly after a 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 check for 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, medications and illicit 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.
Some Causes and Features of Anosmia
Cause | Common Features* | Diagnostic Approach |
|---|---|---|
Blockage within the nose | ||
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 | A doctor's examination alone | |
Polyps that are usually seen during the examination | A doctor's examination alone | |
Destruction of smell receptors‡ | ||
Thin, hard, dry mucous membranes Widened nasal passages Crusting inside the nose A foul-smelling odor in the nose | Sometimes a doctor's examination alone Sometimes a biopsy | |
A thick, foul-smelling nasal discharge most or all of the time Previous sinus infections | Sometimes a doctor's examination alone Usually CT | |
Loss of smell and often symptoms of infection (for example, fever or cough) | Viral testing when available | |
Usually in people who report taking such drugs | A doctor's examination alone | |
Some viral upper respiratory infections (such as influenza) | Loss of smell that occurs after an infection | A doctor's examination alone |
Usually in people who report exposure to such toxins | A doctor's examination alone | |
Tumors (a rare cause) | Possibly vision problems or only loss of smell | MRI or CT |
Destruction of olfactory pathways in the brain | ||
Progressive confusion and loss of recent memory | MRI Neuropsychologic tests§ | |
Brain surgery or a brain infection | In people who have had brain surgery or a brain infection | CT or MRI |
Brain tumors (a rare cause of loss of smell) | Sometimes headache and/or other symptoms of nervous system dysfunction, such as weakness, numbness, or difficulty speaking, seeing, or swallowing | CT or MRI |
Degenerative neurologic disorders (such as multiple sclerosis) | Intermittent episodes of symptoms of nervous system dysfunction, such as weakness, numbness, or difficulty speaking, seeing, or swallowing | MRI Sometimes a spinal tap |
In people who have had a head injury | CT or MRI | |
* Features include symptoms and results of the doctor's examination. Features mentioned are typical but not always present. | ||
† Although a doctor's examination is always done, it is mentioned in this column only if the diagnosis can sometimes be made by the doctor's examination alone, without any testing. | ||
‡ Neuropsychologic testing is detailed testing that covers the main areas of mental function, including memory and mood. | ||
§ Destruction of smell receptors has not yet been confirmed as the mechanism for anosmia. | ||
CT = computed tomography; COVID-19 = coronavirus disease 2019; MRI = magnetic resonance imaging. | ||
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 be tested more formally with 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 COVID-19 is suspected, viral testing is done, and the person is managed according to local protocols, including isolation guidelines.
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 of Anosmia
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 and gas leaks.
Key Points
A loss of smell may be part of normal aging.
Common causes include upper respiratory infections, sinusitis, and head injury.
An imaging test such as CT or MRI is typically needed unless the cause is obvious to the doctor.
