Merck Manual

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Marvin P. Fried

, MD, Montefiore Medical Center, The University Hospital of Albert Einstein College of Medicine

Reviewed/Revised May 2023
Topic Resources

Anosmia is complete loss of smell. Hyposmia is partial loss of smell. If unilateral, anosmia is often unrecognized.

Most patients with anosmia have normal perception of salty, sweet, sour, and bitter substances but lack flavor discrimination, which largely depends on olfaction. Therefore, they often complain of losing the sense of taste (ageusia) and of not enjoying food.

Pathophysiology of Anosmia

Anosmia occurs when

  • Intranasal swelling or other obstruction prevents odors from gaining access to the olfactory area.

  • The olfactory neuroepithelium is destroyed.

  • The olfactory nerve fila, bulbs, tracts, or central connections are destroyed (see table ).


Major causes of anosmia include

Prior upper respiratory infection (URI), especially influenza, is implicated in 14 to 26% of all patients that present with hyposmia or anosmia.

Medications can contribute to anosmia in susceptible patients. Other causes include prior head and neck radiation, recent nasal or sinus surgery, nasal and brain tumors, and toxins. The role of tobacco is uncertain.

Pearls & Pitfalls

  • Immediately urge patients who are at risk of COVID-19 and have suddenly lost their sense of smell to isolate themselves from others.

Evaluation of Anosmia


History of present illness should assess the time course of symptoms and their relation to any URI or head injury. Important associated symptoms are nasal congestion, rhinorrhea, or both. The nature of rhinorrhea should be assessed (eg, watery, mucoid, purulent, bloody).

Review of systems should assess neurologic symptoms, particularly those involving mental status (eg, difficulty with recent memory) and cranial nerves (eg, diplopia, difficulty speaking or swallowing, tinnitus, vertigo).

Past medical history should include history of sinus disorders, cranial trauma or surgery, allergies, use of drugs (prescription, over-the-counter, illicit), and exposure to chemicals or fumes.

Physical examination

The nasal passages should be inspected for swelling, inflammation, discharge, and polyps. Having the patient breathe through each nostril sequentially (while the other is manually occluded) may help identify obstruction.

Red flags

The following findings in patients with anosmia are of particular concern:

  • Head injury

  • Neurologic symptoms or signs

  • Sudden onset

  • Local or global epidemic of COVID-19

Interpretation of findings

A history of chronic rhinosinusitis Sinusitis Sinusitis is inflammation of the paranasal sinuses due to viral, bacterial, or fungal infections or allergic reactions. Symptoms include nasal obstruction and congestion, purulent rhinorrhea... read more Sinusitis suggests that anosmia is caused by chronic rhinosinusitis, particularly when significant congestion, polyps, or both are visible during examination. However, because these findings are common in the population, the physician should be alert to the possibility of another cause (eg, tumor, infection).

Slowly progressive anosmia in an older patient with no other symptoms or findings suggests normal aging as the cause.


An in-office test of olfaction can help confirm olfactory dysfunction. Commonly, one nostril is pressed shut, and a pungent odor such as from a vial containing coffee, cinnamon, or tobacco is placed under the open nostril; if the patient can identify the substance, olfaction is presumed intact. The test is repeated on the other nostril to determine whether the response is bilateral. Unfortunately, the test is crude and unreliable.

If anosmia is present and no cause is readily apparent during clinical evaluation (see table ), patients should have CT of the head (including sinuses) with contrast to rule out a tumor or unsuspected fracture of the floor of the anterior cranial fossa. MRI is also used to evaluate intracranial disease and may be needed as well, particularly in patients with no nasal or sinus pathology seen on CT scans.

A psychophysical assessment of odor and taste identification and threshold detection may help confirm or exclude the presence of anosmia and characterize the type and degree of subjective loss of smell. This assessment commonly involves use of one or several commercially available testing kits. One kit uses a scratch-and-sniff battery of odors; another kit involves sequential dilutions of an odorous chemical.

If COVID-19 is suspected, patients should be tested and managed according to local protocols.

Treatment of Anosmia

Specific causes are treated; however, smell is not always recovered even after successful treatment of sinusitis.

There are no specific treatments for anosmia, except rarely, when the cause is an infection or a medication.

Patients who retain some sense of smell may find adding concentrated flavoring agents to food improves their enjoyment of eating.

Smoke alarms, important in all homes, are even more essential for patients with anosmia. Patients should be cautioned about consumption of stored food and use of natural gas for cooking or heating because they have difficulty detecting food spoilage and gas leaks.

Geriatrics Essentials: Anosmia

There is a significant loss of olfactory receptor neurons with normal aging, leading to a marked diminution of the sense of smell. Changes are usually noticeable by age 60 and can be marked after age 70.

Key Points

  • Anosmia may be part of normal aging.

  • Common causes include URIs, sinusitis, and head trauma.

  • Cranial imaging is typically required unless the cause is obvious.

NOTE: This is the Professional Version. CONSUMERS: View Consumer Version
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