Losing the Sense of Smell: Is the World Only Black and White?
Update Date：2026/03/05，
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Dr. Lin Hung-che
Department of Otolaryngology–Head and Neck Surgery
Common ENT Conditions (Part II)
Losing the Sense of Smell: Is the World Only Black and White?
An ENT Specialist’s Guide to the Diagnosis and Latest Treatments for Olfactory Dysfunction
Column Introduction
Have you ever noticed, after a cold or being diagnosed with COVID-19, that once-aromatic dishes suddenly seem tasteless, or even develop a strange, distorted smell? Olfactory dysfunction does more than just diminish your appetite and culinary enjoyment; it can also lead to social withdrawal and emotional distress. Many patients mistakenly believe their "sense of taste" has deteriorated. However, the tongue is only capable of distinguishing sweet, sour, bitter, salty, and umami. Most of the "flavor" we perceive comes from olfactory stimulation; thus, smell disorders are frequently misidentified as taste problems.
During my advanced studies at Stanford University, I had the privilege of being mentored by the internationally renowned olfactory specialist, Dr. Zara Patel. In this article, I will outline the common clinical types of olfactory dysfunction and the latest treatment strategies to provide the public with a clear understanding and practical guidance.
1.More Than Just "Loss of Smell": Types of Olfactory Dysfunction
Olfactory dysfunction is not limited to simply being unable to smell; some people may experience distorted odors or even phantom smells when no scent is present. Each of these conditions has a specific medical name and treatment approach. While many assume that a "smell problem" only means a complete loss of the sense, the clinical reality is far more diverse. In practice, olfactory dysfunction is generally categorized into the following types:
(1)Anosmia (Total Loss of Smell): The complete inability to detect any odors.
(2)Hyposmia (Decreased Sense of Smell): A reduced ability to perceive or identify odors. This is the most common olfactory issue, where scents feel faint or unclear.
(3)Parosmia (Distorted Sense of Smell): A condition where familiar or pleasant odors are perceived as strange or unpleasant, often resembling the smell of rotten food or garbage.
(4) Phantosmia (Phantom Smells): Perceiving an odor when no actual scent is present, such as constantly smelling smoke or burnt materials. This may be related to olfactory nerve inflammation and, in some cases, requires clinical attention to rule out migraines or other neurological conditions.
Why Do We Lose Our Sense of Smell?There are numerous causes of olfactory dysfunction. In addition to common conditions like sinusitis, nasal polyps, and viral infections such as the common cold, influenza, or COVID-19, several often-overlooked factors can also be responsible:
• Medication Side Effects: Certain chemotherapy drugs, antidepressants, or neurological medications may impact olfactory function.
• Head Trauma: A significant impact to the head can stretch or damage the olfactory nerves, leading to a diminished sense of smell or even total anosmia.
• Early Warning Signs of Neurodegenerative Diseases: A gradual loss of smell can sometimes be one of the earliest clinical manifestations of Alzheimer's disease or Parkinson's disease.
3. The Golden Window for Treatment and Diagnosis: Timing is Key!Although the olfactory nerves possess a certain degree of regenerative capacity, their recovery speed is quite slow. The earlier you receive evaluation and treatment, the higher the chances of restoring your sense of smell. Therefore, if olfactory dysfunction persists for several weeks without improvement, do not delay.
What will the doctor check for?
(1)Medical Evaluation & Diagnostic Procedures
• Nasal Examination: During the clinic visit, an endoscope is typically used to examine the olfactory region deep within the nasal cavity. The physician checks for inflammation, swelling, discharge, or polyps that may be obstructing the path of odor molecules.
• Olfactory Testing: Using scent cards or specialized olfactory testing kits, the physician evaluates whether your sense of smell is functioning normally or has become diminished (hyposmia).
(2) Is Imaging Necessary?
• Depending on the clinical presentation, the physician may arrange for a Computed Tomography (CT) or Magnetic Resonance Imaging (MRI) scan.
• If the loss of smell did not occur following a cold or COVID-19, and there is no prior history of sinusitis (unexplained onset), an MRI is usually considered. This is to rule out the possibility of tumors or other neurological issues.
• In short, delaying the evaluation of olfactory problems not only slows down recovery but may also lead to missing the optimal treatment window. Early examination provides both the best chance for recovery and peace of mind.
4. Evidence-Based Treatments (Things You Can Do at Home)
During my advanced training, I was mentored by the internationally renowned olfactory expert, Dr. Zara Patel. She emphasizes that while there is currently no "magic pill" that can instantly cure olfactory dysfunction, a multimodal treatment approach significantly increases the chances of olfactory recovery.
(1) Olfactory Training: The Most Vital and Safest Rehabilitation Method
Olfactory training can be viewed as "physical therapy for your sense of smell." It is currently the primary first-line treatment with the strongest clinical evidence and the lowest risk. By repeatedly stimulating the olfactory system, you help the olfactory nerves and the brain re-establish connections and awaken "odor memories."
How to perform the rehabilitation?
Initially, you can select four common scents: Rose, Lemon, Eucalyptus, and Clove.
• Frequency: Twice daily (morning and evening).
• Method: Focus intensely while smelling each scent, and try to recall the original memory of that fragrance in your mind.
• Expectation: Olfactory training requires patience and consistency. It typically takes several months of daily practice before progress becomes noticeable.
(2) Steroid Nasal Irrigation: Improving Chronic Inflammation in the Deep Nasal Cavity
Description: Following a medical evaluation, some patients may be prescribed steroid nasal irrigation. This method helps improve the chronic micro-inflammatory environment in the olfactory region, making it easier for odor molecules to reach the olfactory nerves.
(3) Omega-3 Fish Oil Supplementation: Assisting in Neural Repair
• Description: Omega-3 fish oil is currently regarded as a supplementary treatment. Research regarding COVID-19-related olfactory dysfunction suggests that it may aid in neural repair and help reduce chronic inflammatory responses.
• Recommendation: However, fish oil cannot replace standard medical treatment; it is recommended as an adjunctive therapy.
In short, olfactory treatment is a "marathon of patient rehabilitation." The earlier you begin and the more consistently you practice, the higher the likelihood of improvement. If symptoms persist or worsen, you should seek a further evaluation by an ENT specialist.
5. Cutting-Edge Medical Technology: PRP Injection (Considered After Medical Evaluation)
For patients whose loss of smell has persisted for an extended period and who show limited response to conventional treatments—such as olfactory training, medications, or nasal irrigation—Platelet-Rich Plasma (PRP) injection has emerged in recent years as a promising adjunctive treatment option.
PRP is extracted from the patient’s own blood to produce a high concentration of platelets, which contain various growth factors. These factors are utilized to improve the regenerative environment surrounding the olfactory nerves. According to randomized controlled trials (RCTs), patients suffering from long-term olfactory loss following COVID-19 who received PRP treatment showed a significantly higher probability of improvement compared to untreated or placebo groups.
It is important to emphasize that PRP is not an "instant fix." Its effects are typically gradual and progressive. Currently, it serves primarily as an adjunctive intervention for those who have not responded well to standard therapies. Whether a patient is a suitable candidate for PRP must be determined through a comprehensive evaluation by an ENT specialist.
Conclusion: Do Not Give Up Hope
The repair of olfactory nerves often takes time; it frequently requires several months, or even half a year or more, for progress to gradually manifest. Even if the loss of smell has persisted for years, through olfactory training, nasal irrigation, and—where appropriate—treatments like PRP, there is still an opportunity to gradually restore a portion of your sense of smell. Regaining this sense allows you to experience the flavors of food and the vibrant colors of life once again. If olfactory issues continue to affect your quality of life, we recommend consulting with a specialist to determine the treatment strategy that best suits your needs.
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