Loss of smell, known medically as anosmia, can be caused by various illnesses. Anosmia can be temporary or permanent depending on the underlying cause.
Common Causes of Anosmia
Some common causes of temporary anosmia include:
- Common cold – Viruses that cause the common cold can result in temporary loss of smell. This normally resolves within 1-2 weeks as the cold improves.
- Allergies – Swelling and inflammation in the nasal passages from allergies can block odor molecules from reaching the smell receptors. Treatment of the allergies can help restore normal smell.
- Nasal and sinus problems – Conditions like nasal polyps or chronic sinusitis can block airflow and prevent smells from reaching smell receptors. Surgery may be needed to remove polyps and treat sinus disease.
- Influenza – Upper respiratory infections from the flu virus can cause temporary loss of smell. Smell typically returns when the flu resolves, within 1-2 weeks.
Some common causes of permanent or long-term anosmia include:
- Head trauma – Injuries that sever the olfactory nerves can cause permanent loss of smell. Damage to areas of the brain related to smell can also cause long-term anosmia.
- Chronic rhinosinusitis – Prolonged nasal/sinus inflammation from conditions like hay fever or nasal polyps can damage smell receptors.
- Neurodegenerative diseases – Diseases like Alzheimer’s and Parkinson’s interfere with brain regions linked to olfaction.
- Exposure to toxic chemicals – Fumes from chemicals like insecticides and metals can damage nerves involved in the sense of smell.
How COVID-19 affects smell
Loss of smell is a common symptom in up to 80% of people infected with COVID-19. The SARS-CoV-2 virus is thought to cause temporary damage to the olfactory nerves responsible for detecting odors.
In most people, smell recovers within 4 weeks of other COVID symptoms resolving. However, some studies have found that up to 10% of people have not regained their sense of smell 6 months after a COVID diagnosis.
The prolonged loss of smell seen in some COVID patients has been termed “post-viral olfactory dysfunction.” It can be caused by damage to the olfactory nerves as well as ongoing inflammation in the nasal cavity.
Why COVID causes loss of smell
Research shows the SARS-CoV-2 virus can invade and damage the olfactory neurons in the nasal cavity in several ways:
- The virus directly invades and destroys the olfactory sensory neurons
- It damages sustentacular cells that support the olfactory neurons
- It triggers a damaging immune response and inflammation
This impairs the ability to transmit and detect odor signals from the nose to the brain, resulting in loss of the sense of smell.
How is anosmia diagnosed?
To evaluate anosmia, doctors typically use smell tests like:
- UPSIT – This is the University of Pennsylvania Smell Identification Test. It involves 40 different “scratch and sniff” odors. The patient identifies each by choosing from four options.
- Sniffin’ Sticks – Felt-tip pens containing different odors are placed under the nose. The patient indicates when they detect the smell.
- Brief Smell Identification Test – This tests the ability to detect 12 common odors like orange, leather, and strawberry.
These tests help determine the degree of smell loss and pinpoint areas of difficulty. Doctors may also use endoscopies or CT/MRI scans to visualize the nasal passages and olfactory nerves.
Treatments for Anosmia
Treatment options for smell loss depend on the underlying cause. Some strategies include:
- Steroids – Nasal spray steroids can reduce inflammation in the nasal passages caused by infections, allergies, or immune issues. This may help restore airflow and smell.
- Oral steroids – Oral steroid pills are sometimes prescribed for short-term smell loss, like from a respiratory infection.
- Smell training – This involves sniffing 4 odors (e.g. lemon, rose, clove, eucalyptus) twice daily for months. It may help regenerate olfactory nerves.
- Surgery – Surgery to remove obstructions like nasal polyps can improve anosmia caused by structural blockages.
Antiviral medications are being studied for utility in treating smell loss after COVID-19. However, currently there are no proven treatments for post-COVID anosmia specifically.
Coping with Anosmia
Loss of smell can negatively impact quality of life. Coping strategies for anosmia include:
- Using scent-free personal hygiene products to avoid irritation
- Adding texture and flavor to foods through spices, herbs, etc.
- Ensuring proper gas/smoke alarm function in the home
- Avoiding spoiled foods by closely monitoring expiration dates
- Seeking counseling for depression/anxiety related to the loss
Joining a support group can also provide validation and advice. However, any changes in smell should prompt a doctor visit to identify the cause.
Outlook for Anosmia
The prognosis for anosmia depends greatly on the cause:
- Viral infections – Smell typically recovers fully within weeks as the infection resolves.
- Allergies – Sense of smell improves with treatment of the allergy symptoms.
- Nasal polyps – Removing polyps often restores smell if no permanent damage is done.
- Neurodegenerative disease – Smell loss is usually permanent due to progressive nerve damage.
- Head trauma – Smell may recover over time if nerves regenerate, but can be permanent.
- COVID-19 – Most regain smell within weeks, but some may experience months of dysfunction.
With proper treatment tailored to the cause, many types of anosmia are reversible if olfactory nerves are still intact. But permanent damage to the olfactory nerves predicts irreversible smell loss in most cases.
When to See a Doctor
See a doctor promptly if you experience:
- Sudden loss of smell without nasal congestion or allergies
- Loss of smell with significant nasal blockage or discharge
- Smell loss following an injury or head trauma
- Persistent loss of smell lasting longer than 1-2 weeks
Rapid evaluation and treatment of anosmia provides the best chance for regaining smell function. Seek emergency care for smell loss after any head injury.
Key Points
- Anosmia refers to partial or complete loss of smell.
- Common causes include respiratory infections, allergies, nasal polyps, head trauma, or neurologic disease.
- Smell loss is a primary symptom of COVID-19 infection.
- Diagnosis often uses smell identification tests along with imaging studies.
- Treatments can include nasal steroids, surgery, and smell training therapy.
- Prognosis varies; some causes result in permanent loss, while others are temporary.
- Sudden or persistent smell loss warrants medical evaluation.
Frequently Asked Questions
Can anxiety cause loss of smell?
Anxiety itself does not directly impair the sense of smell. However, chronic stress and anxiety can sometimes contribute to temporary smell loss in a few ways:
- Chronic stress may make people more prone to viral upper respiratory infections that can cause temporary anosmia.
- Anxiety could potentially trigger inflammation in nasal cavities and impede airflow needed to smell.
- Attention and perception of odors may be impaired due to anxiety consuming mental resources.
Treatment of the underlying anxiety could potentially help resolve any associated issues with smell. But anxiety is not a primary known cause of true anosmia.
Can a sinus infection cause loss of smell?
Yes, sinus infections can frequently cause loss of smell. Sinusitis refers to inflammation of the sinuses caused by an infection or allergy. Swelling in the sinus cavities can obstruct airflow, preventing odor molecules from reaching smell receptors. Congestion from the infection also blocks smell. Treatments like nasal steroid sprays, antihistamines, decongestants, and antibiotics can help resolve sinus infection-related anosmia.
Can you get your smell back after losing it?
The ability to regain smell after losing it depends on the underlying cause. Smell loss from temporary causes like viruses and nasal polyps is often reversible once the issue resolves or is treated. Permanent damage to olfactory nerves from head trauma, chronic sinusitis, or neurodegenerative disease may not allow smell to fully return. COVID-related smell loss is usually temporary but can sometimes last months or be permanent. With proper diagnosis and management, many types of smell loss can be improved or reversed.
At what age do you start losing your sense of smell?
Normal age-related decline in the sense of smell is called presbyosmia. It often begins around age 60 and becomes more notable in the 70s and beyond. Gradual damage to olfactory nerves and loss of epithelial cells in the nasal cavity caused by aging leads to reduced smell sensitivity. Around half of people ages 65-80 have some degree of measurable smell loss. Severe loss of smell function is rare before the 60s unless there is a specific medical cause.
How can you detect early signs of Alzheimer’s?
Some early signs that may indicate Alzheimer’s disease include:
- Mild memory loss impacting daily life
- Increasing confusion and disorientation
- Difficulty planning or problem-solving
- Changes in mood and personality
- Loss of smell
- Problems with language and writing
- Misplacing items often
- Unable to retrace steps or follow directions
Loss of the sense of smell can occur years before memory and thinking problems emerge. If smell dysfunction cannot be attributed to another cause like a sinus infection, it may warrant evaluation for Alzheimer’s. Early diagnosis allows the best opportunity to start treatment and plan for the future.
Conclusion
Loss of smell can result from various temporary or permanent conditions affecting the nasal passages or brain. While the prognosis depends on the cause, treatments are available that may help restore smell function.Sudden or unexplained smell loss should prompt medical evaluation to identify any underlying issues requiring treatment. With an understanding of the cause and strategic management, it may be possible to regain smell sensation that was lost.