Smell disorders are problems in which odors cannot be detected at all, are sensed weakly or are perceived differently from how they really are, and they are far more common than most people think. Nasal congestion, sinusitis, viral infections, head injuries and aging are among the main causes. Because the sense of smell supports not only the enjoyment of pleasant scents but also taste and the ability to notice dangers such as gas leaks, smoke and spoiled food, this complaint deserves careful evaluation.
What Are Smell Disorders?
Smelling begins in a small area at the very top of the nasal cavity, roughly level with the space between the eyes. The special lining covering this area contains nerve cells sensitive to odors. When odor molecules in inhaled air reach this region and dissolve in the mucus layer, these nerve cells are stimulated. The signal travels through nerve fibers passing through a thin bony plate in the roof of the nose to the olfactory bulb just above, and from there to the smell centers of the brain.
Smell nerve cells are among the few nerve cells in the body that can regenerate. This explains why some types of smell loss can improve on their own within months. However, this capacity for renewal declines with age.
Much of the flavor we get from food also comes from smell. While chewing, odor molecules rise from the mouth toward the back of the nose and reach the smell area from behind. That is why many people who lose their sense of smell say that “food has no taste,” even though their perception of sweet, salty, sour and bitter on the tongue is usually preserved.
Types of Smell Disorders
- Anosmia: Complete loss of the sense of smell.
- Hyposmia: A reduced sense of smell; the most common type.
- Parosmia: Odors are perceived differently, usually as unpleasant or disturbing; for example, coffee may smell burnt or rotten.
- Phantosmia: Sensing a smell that is not present, a “phantom smell.”
- Hyperosmia: Heightened sensitivity to odors; it can occur during pregnancy and migraine attacks.
Smell loss can occur at any age, but it becomes considerably more common with age. A significant proportion of people over sixty have a reduced sense of smell, often without being aware of it. It is also more common in smokers and in people with chronic sinusitis and nasal polyps.
Causes of Smell Disorders
Causes are generally grouped into two categories. In the first, odor molecules cannot reach the smell area; in the second, the molecules arrive but there is damage to the nerve cells, the nerve pathways or the brain. Both mechanisms may be present in the same patient.
When Odors Cannot Reach the Smell Area (Conductive Type)
- Chronic sinusitis and nasal polyps, among the most common causes of smell loss, which often respond well to treatment
- Swelling of the lining in allergic and non-allergic rhinitis
- Structural narrowing such as a deviated septum or enlarged turbinates
- Tumors of the nose and sinuses, which are rare
- Scar bands from previous nasal surgery
When the Nerves Are Damaged (Sensorineural Type)
- Viral infections: Smell loss after a cold, flu or COVID-19 is among the most frequent causes. The virus can affect the support cells and nerve cells in the smell area.
- Head injury: Sudden smell loss can develop when the fine nerve fibers passing through the roof of the nose are damaged by a blow.
- Aging: The number of smell nerve cells and their rate of renewal decline.
- Neurological diseases: In Parkinson’s and Alzheimer’s disease, smell loss may appear years before other symptoms.
- Toxic substances and medications: Certain chemicals, heavy metals, smoking, some antibiotics and chemotherapy drugs can affect the sense of smell, as can radiation therapy to the head and neck.
- Congenital absence of smell: Rare; it is sometimes associated with hormonal development disorders.
Systemic conditions such as diabetes, thyroid disease and kidney or liver failure can also affect the sense of smell. In some patients, no specific cause is found despite thorough investigation.
Symptoms of Smell Disorders
The most obvious complaint is a reduced or lost ability to detect odors, but many people first notice it as a “loss of taste.” Symptoms may develop gradually or begin suddenly after an infection or a blow to the head.
- Being unable to smell, or only faintly smelling, everyday odors such as perfume, food or coffee
- Food tasting bland, with related changes in appetite
- Odors seeming repulsive, burnt, rotten or chemical
- Sensing smells that are not there
- Being unable to notice smoke, gas leaks or spoiled food
- Worries about personal hygiene and discomfort in social settings
Accompanying symptoms offer clues to the cause. Nasal congestion, thick discharge and facial pressure suggest sinusitis or polyps, while seasonal complaints point to allergy. Smell loss that fluctuates during the day suggests a conductive problem, whereas a constant and complete loss suggests nerve damage. Parosmia often appears during recovery after a viral infection and is frequently part of the nerve regeneration process.
Smell loss affects quality of life more than many people expect. Loss of enjoyment of food, weight changes, feeling unsafe and anxiety or low mood are more common in these patients. Psychological effects should therefore be part of the evaluation.
How Are Smell Disorders Diagnosed?
Evaluation begins with detailed questions about when and how the complaint started. A preceding infection, head injury, medications, chemicals in the workplace, smoking, nose and sinus complaints and any neurological symptoms are all important.
During the ENT (ear, nose and throat) examination, the inside of the nose, especially the upper part where the smell area lies, is examined with nasal endoscopy. The doctor looks for polyps, inflamed lining, thick mucus, a deviated septum or a mass. Endoscopy reveals most conductive causes.
When needed, the following tests are used:
- Smell tests: Standardized test kits in the form of pens or scratch-and-sniff cards measure the smell threshold and the ability to distinguish and identify odors. They quantify the degree of loss and allow improvement to be tracked during follow-up.
- CT scan: Used to evaluate sinus disease and blockage of the smell area.
- MRI: May be requested to examine the olfactory bulb and brain structures after a head injury, when the loss is unexplained or when neurological symptoms are present.
- Blood tests: Done when systemic causes such as diabetes, thyroid problems or vitamin deficiencies are suspected.
- Allergy tests: Support the diagnosis when allergic rhinitis is suspected.
Patients traveling from abroad are encouraged to bring any previous smell test results, CT or MRI images and a list of their current medications.
Treatment of Smell Disorders
Treatment is planned according to the cause and duration of the smell loss. Conductive problems generally have a better chance of improvement; with nerve-related loss, recovery may be slower and varies widely from person to person.
Medication
Corticosteroid nasal sprays are the mainstay of treatment for smell loss due to chronic sinusitis, polyps and allergy. To help the spray reach the smell area, using it with the head bent forward or tilted back may be recommended. In patients with significant polyps, a short course of oral steroids can bring a rapid improvement in smell; however, keeping that benefit requires long-term control of the underlying disease. Saline nasal rinsing supports treatment by clearing mucus.
Smell Training
Smell training is one of the most frequently recommended methods for smell loss after a viral infection or head injury. Typically, four clearly different scents, such as rose, lemon, eucalyptus and clove, are sniffed attentively twice a day for about half a minute each. While sniffing, the person tries to recall what that smell is like. Training is continued for at least 12 weeks and often longer.
Smell training is easy to do and has no side effects. Although studies have reported varying results, it is thought to support recovery in many patients. The scents can be changed at intervals as training continues.
Surgical Treatment
If chronic sinusitis and polyps that do not respond to medication block airflow to the smell area, endoscopic sinus surgery may be performed. Done under general anesthesia, it usually takes 1–2 hours; patients generally go home the same day and can return to daily life within 1–2 days. Structural problems such as a deviated septum or enlarged turbinates can be corrected in the same session. Improvement in smell after surgery depends on how long the loss has lasted and how extensive the disease is.
Recovery After a Viral Infection
A large proportion of smell loss after a cold, flu or COVID-19 improves on its own within weeks or months. In some patients, recovery may take a year or longer. Parosmia is common during this period and usually fades over time. Regular smell training and periodic follow-up testing help track recovery.
Possible Risks and Important Considerations
The most important risk for people with smell loss is failing to notice dangers in time. Some safety measures are therefore important:
- Using gas and smoke detectors at home
- Checking expiration dates and not eating food that seems questionable
- Using a timer when cooking on the stove
- Not mixing cleaning products and using them in well-ventilated areas
- Avoiding adding too much salt and sugar to food to make up for reduced taste
Taking steroids on your own for long periods or turning to products with no proven effect can do more harm than good. It is recommended that treatment be planned after an evaluation by an ENT specialist.
Seek an examination without delay in the following situations:
- Sudden smell loss with no obvious cause
- Smell loss after a head injury
- Smell loss together with one-sided nasal blockage, bloody discharge or facial numbness
- Accompanying neurological symptoms such as forgetfulness, tremor, headache or vision changes
- Smell loss lasting more than two weeks with no sign of improvement
Smell Disorders: Frequently Asked Questions
Will my sense of smell come back?
It depends on the cause. Loss due to polyps, sinusitis or allergy often improves with treatment. Most smell loss after viral infections improves over time, while recovery may be more limited when the loss is due to head injury or aging.
How long does smell loss after COVID-19 last?
In most patients, smell returns within a few weeks. In some, it can last for months, and odors may be perceived differently for a while during recovery. People whose complaint persists are advised to have an ENT examination and start smell training.
What conditions can smell loss be a sign of?
The most common causes are sinusitis, polyps, allergy and viral infections. Less often, it can be seen with head injuries, nasal tumors and neurological diseases such as Parkinson’s. That is why long-lasting smell loss should always be evaluated.
Why do I smell something bad when nothing is there?
Sensing odors that are not present is called phantosmia. It can be caused by sinusitis, dental or mouth infections, the recovery process after a viral infection or, more rarely, neurological causes. An ENT examination is needed for evaluation.
Does quitting smoking improve the sense of smell?
Smoking damages the cells in the smell area and dulls the sense of smell. Many people who quit smoking notice that their ability to smell partly improves over time.
Conclusion
Op. Dr. Tayfun Demirel, ENT specialist, evaluates patients experiencing smell loss or changes in smell perception at the practice in Ataşehir, Istanbul, using endoscopic examination and the necessary tests. Once the cause is identified, medication, smell training or, when needed, surgical options are planned individually, and recovery is monitored with regular check-ups. Please contact the clinic to book an appointment. This article is for informational purposes only; an in-person examination is required for diagnosis and treatment.
