Table: Some Causes and Features of Anosmia - Merck Manuals Consumer Version

Some Causes and Features of Anosmia

Cause	Common Features^*	Diagnostic Approach
Blockage within the nose
Nasal allergies Seasonal Allergies Seasonal allergies result from exposure to airborne substances (such as pollens) that appear only during certain times of the year. Seasonal allergies cause itchy skin, a runny nose, sneezing... read more	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
Nasal polyps Nasal Polyps Nasal polyps are fleshy outgrowths of the mucous membrane of the nose. Nasal polyps are more likely to develop in people who have allergies or asthma. Some of the symptoms caused by polyps are... read more	Polyps that are usually seen during the examination	A doctor's examination alone
Destruction of smell receptors
Chronic sinusitis Chronic sinusitis Sinusitis is inflammation of the sinuses, most commonly caused by a viral or bacterial infection or by an allergy. Some of the most common symptoms of sinusitis are pain, tenderness, nasal congestion... read more	A thick, foul-smelling nasal discharge most or all of the time Previous sinus infections	Sometimes a doctor's examination alone Usually computed tomography (CT)
Coronavirus disease 2019 ( COVID-19 COVID-19 COVID-19 is an acute respiratory illness that can be severe and is caused by the coronavirus named SARS-CoV-2. Symptoms of COVID-19 vary significantly. Two types of tests can be used to diagnose... read more )‡	Loss of smell is often followed by other symptoms of infection (for example, fever or cough)	Viral testing when available
Drugs (such as amphetamines, enalapril, estrogen, naphazoline, phenothiazines, and reserpine or use of decongestants for a long time)	Usually in people who report taking such drugs	A doctor's examination alone
Some viral upper respiratory infections (such as influenza Influenza (Flu) Influenza (flu) is a viral infection of the lungs and airways with one of the influenza viruses. It causes a fever, runny nose, sore throat, cough, headache, muscle aches (myalgias), and a general... read more )	Loss of smell that occurs after an infection	A doctor's examination alone
Toxins (such as cadmium and manganese)	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	Magnetic resonance imaging (MRI) or CT
Destruction of olfactory pathways in the brain
Alzheimer disease Alzheimer Disease Alzheimer disease is a progressive loss of mental function, characterized by degeneration of brain tissue, including loss of nerve cells, the accumulation of an abnormal protein called beta-amyloid... read more	Progressive confusion and loss of recent memory	MRI Neuropsychologic (for example. memory) tests
Brain surgery or infection Brain Infections	In people who have had brain surgery or a brain infection	CT or MRI
Brain tumors Overview of Brain Tumors A brain tumor can be a noncancerous (benign) or cancerous (malignant) growth in the brain. It may originate in the brain or have spread (metastasized) to the brain from another part of the body... read more	Sometimes headache and/or symptoms of nervous system dysfunction	CT or MRI
Degenerative neurologic disorders Multiple Sclerosis (MS) and Related Disorders (such as multiple sclerosis)	Intermittent episodes of other symptoms of nervous system dysfunction, such as weakness, numbness, or difficulty speaking, seeing, or swallowing	MRI Sometimes a spinal tap
Head injuries Head Injuries	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. ‡ Destruction of smell receptors has not yet been confirmed as the mechanism for anosmia.