Loss of Smell: Causes, Treatment, and Smell Retraining Therapy
By: Dr. Madeleine Samuelson Herman, MD, MPH
Whether it’s caused by a cold, COVID-19, allergies, or chronic sinus disease, losing your sense of smell stinks.
I frequently talk to patients about loss of smell (anosmia) and changes in their ability to smell, also known as olfactory dysfunction. Some people completely lose their sense of smell, while others notice that smells have become weaker, distorted, or different than they remember.
Your sense of smell is closely connected to your sense of taste, appetite, memories, and even your ability to detect potential dangers such as smoke or spoiled food. So when your sense of smell changes, it can have a surprisingly significant impact on your quality of life.
What Causes Loss of Smell?
There are many potential causes of anosmia and other smell disorders. Some are temporary and improve on their own, while others require medical evaluation and treatment.
#1 COVID-19
COVID-19 became well known for causing a sudden loss of smell and taste. While smell loss is less common with newer COVID variants than it was early in the pandemic, it remains an important cause of post-viral smell dysfunction.
COVID-related smell loss is thought to result primarily from inflammation and injury involving the supporting cells of the olfactory system rather than the virus directly destroying the smell-sensing nerve cells.
Most people recover their sense of smell, but some experience persistent or altered smell for months or longer.
#2 Post-Viral Smell Loss
COVID-19 isn't the only virus that can affect your sense of smell.
Common upper respiratory infections and other viruses can cause post-viral olfactory dysfunction, sometimes leaving patients with a reduced or completely absent sense of smell after the infection has resolved.
Some patients experience parosmia, in which familiar smells suddenly smell distorted, unpleasant, or completely different than they remember. For example, coffee, onions, meat, or other foods may develop a burnt, rotten, or chemical-like smell.
Fortunately, many patients gradually improve with time, and smell retraining therapy may be helpful for some people.
#3 Head Trauma
Head injuries can also cause permanent or temporary changes in the sense of smell.
The olfactory nerves are made up of tiny nerve fibers that travel from the upper portion of the nose through the skull to the brain. Significant head trauma can damage or shear these delicate nerve fibers.
Smell loss following a head injury deserves medical evaluation, particularly if it is persistent or accompanied by other neurologic symptoms.
#4 Nasal Obstruction and Sinus Disease
Sometimes the problem isn't with the smell nerves themselves—it's that odors can't reach them.
Conditions that cause inflammation or blockage inside the nose can interfere with the ability of odor molecules to reach the olfactory region at the top of the nasal cavity.
Potential causes include:
Chronic sinusitis
Nasal polyps
Allergic rhinitis
Significant nasal congestion
Deviated nasal septum
Other structural problems inside the nose
If you have chronic nasal congestion and decreased smell, treating the underlying sinus or nasal disease may improve your sense of smell.
#5 Medications, Tobacco, and Chemical Exposure
Certain medications and environmental exposures can affect the sense of smell.
Potential contributors include tobacco smoke, some medications, and exposure to certain industrial chemicals or solvents.
If you notice a change in your sense of smell after starting a medication or following significant chemical exposure, discuss it with your physician rather than stopping a prescribed medication on your own.
#6 Nutritional Deficiencies
Certain nutritional deficiencies have been associated with changes in smell and taste. Zinc deficiency, for example, can affect normal sensory function.
However, taking zinc supplements isn't appropriate for everyone with smell loss. Excessive zinc can itself cause problems, so supplementation should be discussed with your physician and guided by your individual circumstances.
#7 Neurologic Conditions
Changes in the sense of smell can sometimes be associated with neurologic disorders.
Reduced smell has been reported in conditions including Parkinson's disease and Alzheimer's disease, among others. In some cases, a decreased sense of smell can occur before other symptoms become apparent.
This does not mean that everyone with smell loss has a neurologic disease. There are many much more common causes of anosmia, including viral infections, allergies, and sinus disease.
However, unexplained, persistent, or progressive smell loss deserves appropriate evaluation.
How Is Loss of Smell Diagnosed?
If you've experienced a significant or persistent change in your sense of smell, talk with your physician or an ENT (ear, nose, and throat specialist).
Your evaluation may include:
A detailed medical history
Examination of the nose and nasal passages
Nasal endoscopy when appropriate
Evaluation for allergies or chronic sinus disease
Review of medications and environmental exposures
Formal smell testing in selected patients
Imaging such as a CT scan or MRI when clinically indicated
The goal is to determine why your sense of smell has changed and whether there is a treatable underlying cause.
How Is Loss of Smell Treated?
Treatment depends on the underlying cause.
For example, if allergies or chronic sinus inflammation are contributing to your smell loss, treating the inflammation may help restore olfactory function. Patients with nasal polyps, significant structural abnormalities, or other forms of obstructive nasal disease may benefit from medical or surgical treatment.
In other cases, the smell loss may be related to a viral infection, head trauma, medication, or neurologic condition and may require a different approach.
Because there are so many potential causes of anosmia, there is no single treatment that works for everyone.
Smell Retraining Therapy
One treatment that may help some patients with persistent post-viral smell loss is smell retraining therapy (SRT), also called olfactory training.
The concept is simple: repeatedly expose yourself to several distinct odors while intentionally concentrating on what each smell should be like.
The goal is to repeatedly stimulate the olfactory system and encourage the brain to recognize and process those odors.
How to Perform Smell Retraining Therapy
A traditional smell-training routine uses at least four different scents representing different odor categories. Commonly used scents include:
Rose – floral
Lemon – fruity
Clove – spicy
Eucalyptus – resinous
You don't necessarily need a specialized kit. You can use essential oils or other familiar, safe household scents.
Step-by-Step Smell Training
Choose four distinct scents.
Smell each scent individually for approximately 10–20 seconds.
While smelling, concentrate on what you remember the scent smelling like.
Take a short break between scents.
Repeat the process once or twice each day.
Continue consistently for at least 12 weeks.
Consistency is important. Some people notice improvement quickly, while for others, recovery can take considerably longer.
You can also change the scents periodically to expose your olfactory system to different odors.
Don't Get Discouraged
One of the hardest parts of smell retraining is patience.
You may not notice an immediate improvement. Some people experience gradual changes, while others may notice that certain smells begin returning before others. Some patients may also experience distorted smells during recovery.
The important thing is to remain consistent and understand that olfactory recovery can take time.
When Should You See an ENT for Loss of Smell?
If your sense of smell suddenly disappears or remains significantly reduced after an illness, injury, or for no obvious reason, it's worth discussing with your physician.
An ENT can evaluate your nose and sinuses to determine whether there is an obstructive or inflammatory cause that can be treated.
You should especially consider an evaluation if your smell loss is:
Persistent or worsening
Associated with chronic nasal congestion
Associated with recurrent sinus infections
Accompanied by nasal polyps
Following a significant head injury
Associated with other neurologic symptoms
Occurring without an obvious explanation
Your Sense of Smell Matters
Loss of smell is more than just an inconvenience. It can affect your enjoyment of food, appetite, memories, quality of life, and ability to detect environmental hazards.
The good news is that many causes of smell loss are treatable, and some patients recover naturally over time.
If you've lost your sense of smell or noticed that smells don't seem quite right, don't just assume you have to live with it. An evaluation by an ENT can help determine the cause and identify appropriate treatment options.
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