Evaluation of olfactory loss

Overview 
Theory 
Emergencies 
Diagnosis 
Resources 

Last reviewed: 25 Mar 2025

Last updated: 15 Apr 2025

Olfactory loss has been linked to a variety of causes and can profoundly influence a patient's quality of life.

Epidemiology

It is estimated that olfactory dysfunction affects approximately 22% of the general population; however, estimated prevalence rates vary significantly according to assessment techniques used, definitions of impairment, and the population sampled.[1][2]

Prevalence of olfactory impairment increases with age and male sex; some degree of olfactory dysfunction may be present in more than 50% of adults ages over 65 years.[1][3][4][5] In one cross-sectional sample of American adults with mean age 68 years, approximately 22% were unable to identify four or more odors using a validated odor identification task.[6] Older African-Americans and Hispanic Americans were more likely to suffer from age-related olfactory dysfunction than white Americans.[6]

Olfactory dysfunction prevalence estimates are generally higher when psychophysical (objective) tools, rather than subjective assessment techniques, are used to assess olfactory dysfunction.[1][4][5][7]

Severe olfactory dysfunction or complete olfactory loss (anosmia) is relatively uncommon in the general population. Prevalence estimates generally range from approximately 1% to 5% of the general population.[8][9]

COVID-19 pandemic

The global COVID-19 pandemic has significantly impacted prevalence rates of olfactory dysfunction, creating an additional cohort of people affected by both acute and postinfectious impairment or loss of olfactory function.[1]

Systematic reviews and cohort studies have reported olfactory dysfunction prevalence of between 48% and 86% in COVID-19 patients.[10][11][12] Prevalence of chemosensory dysfunction in patients with COVID-19 appears to differ between populations and ethnicities.[13][14][15]

Etiology

In patients presenting primarily for loss of smell, the most commonly identified etiologies include a prior viral upper respiratory infection, head trauma, and underlying chronic sinus inflammation.[16][17][18] These 3 causes account for over 50% of patients.

Pathophysiology

Olfactory loss may occur as a sensorineural loss, following degenerative changes in the olfactory neuronal receptors or neuroepithelium in the olfactory cleft.[19] It may also occur as a conductive loss following an obstruction or inflammation within the nasal vault that prevents access of odorants to the olfactory receptors.

Types of olfactory loss

The loss may be complete (anosmia) or partial (hyposmia). It may be associated with perceived odor distortions (dysosmia) that are related to actual environmental odorant stimulation (parosmia) or occur spontaneously (phantosmia).

Presentation

Patients may present complaining of both smell and taste loss, or isolated taste loss, but on investigation their taste function is intact. This relates to the common confusion between taste and flavor. Taste sensation includes salt, sour, sweet, bitter, and umami (savory).[20] Flavor perception is based upon olfactory, tactile, and thermal sensations as well as taste, with olfactory being arguably the most important of these sensations. The loss of olfactory input makes food generally unappealing, something most patients notice very quickly. However, a true measurable taste loss is distinctly uncommon.[16]

Treatment

For patients with olfactory loss due to an inflammatory process, reducing inflammation and obstruction in the nasal vault can effectively restore the ability to smell.[21]

Unfortunately, in most cases of olfactory loss, no specific therapy is available. However, patients will continue to seek medical opinion until they feel a thorough workup has been performed and a thorough explanation has been provided.[22] Some data suggest that olfactory training can increase the potential recovery after a postviral or post-traumatic olfactory loss.[23][24]

Adverse sequelae

Safety issues related to olfactory loss include the inability to detect gas leaks, fire, or spoiled foods. However, the most significant impact for each patient is typically the loss in quality of life related to eating and drinking.[1][25] This can be devastating. In some cases it may result in diminished appetite and inadequate nutritional intake, and in other cases it can cause increased oral intake and weight gain as patients seek chemosensory satisfaction. These consequences can have a negative impact on associated medical conditions such as diabetes and high blood pressure. Invariably, patients receive little sympathy from friends and, on occasion, family and sometimes even from their physician.

For most patients who experience a loss of smell, no restorative therapy is available (unless the loss is secondary to inflammatory rhinosinusitis). Therefore, while most patients do benefit from counseling regarding safety issues and flavor enhancement methods, any information regarding prognosis becomes very important. Studies suggest prognosis relates more to the severity of the initial loss (as confirmed on objective olfactory testing), the age and sex of the patient, smoking, and the presence of dysosmia, than to the etiology of sensorineural loss.[26][27]

Differentials

Common

Viral upper respiratory infection
Nasal polyps
Chronic inflammatory sinus disease
Frontal or occipital trauma
Concussive injury caused by frontal or occipital blow to head
Aging

Full details

Uncommon

Chemical exposure
Drug exposure
Radiation therapy of head and neck
Alzheimer disease
Parkinson disease
Anterior craniotomy
Craniofacial procedures
Endoscopic sinus surgery
Granulomatosis with polyangiitis
Sarcoidosis
Sjogren syndrome
Sinonasal tumors
Esthesioneuroblastoma
Olfactory groove meningioma
Turner syndrome
Kallmann syndrome

Full details

Contributors

Authors

Allen M. Seiden, MD, FACS

Professor of Otolaryngology - Head and Neck Surgery

University of Cincinnati

Cincinnati

Disclosures

AMS has received financial reimbursement from his employer for attending scientific/educational meetings. AMS is an author of a number of references cited in this topic.

Peer reviewers

Spencer C. Payne, MD

Associate Professor of Otolaryngology - Head & Neck Surgery

University of Virginia

Charlottesville

Disclosures

all disclosures

Sangeeta Kapur Maini, MS, DNB, DLO(RCS), FRCS(Ed), FRCS (ORL)

ENT Consultant and Honorary Senior Lecturer

University of Aberdeen

Department of Otolaryngology Head and Neck Surgery

Aberdeen Royal Infirmary

Aberdeen

Disclosures

SKM declares that she has no competing interests.

Simon Gane, MB, BS, DLO(RCS), FRCS (Ed)

ENT Consultant

Royal National Throat, Nose, and Ear Hospital

London

Disclosures

SG declares that he has no competing interests.

Eric H. Holbrook, MD

Massachusetts Eye and Ear Infirmary

Harvard Medical School

Boston

Disclosures

EHH declares that he has no competing interests.

Patient information
Alzheimer's disease and other kinds of dementia
Parkinson disease: what is it?
More Patient information
Log in or subscribe to access all of BMJ Best Practice

Use of this content is subject to our disclaimer

Evaluation of olfactory loss

Summary

Epidemiology

Etiology

Pathophysiology

Types of olfactory loss

Presentation

Treatment

Adverse sequelae

Differentials

Common

Uncommon

Contributors

Authors

Allen M. Seiden, MD, FACS

Disclosures

Peer reviewers

Spencer C. Payne, MD

Disclosures

Sangeeta Kapur Maini, MS, DNB, DLO(RCS), FRCS(Ed), FRCS (ORL)

Disclosures

Simon Gane, MB, BS, DLO(RCS), FRCS (Ed)

Disclosures

Eric H. Holbrook, MD

Disclosures

Patient information

Log in or subscribe to access all of BMJ Best Practice

Log in or subscribe to access all of BMJ Best Practice

Log in to access all of BMJ Best Practice