Hyposmia: Symptoms, Types, Causes and Treatment

Hyposmia—the partial loss of the sense of smell—can profoundly impact quality of life, yet it often goes unrecognized compared to other sensory deficits. From subtle changes in food enjoyment to critical early signs of neurodegenerative diseases, hyposmia is a window into both nasal and neurological health. In this article, we’ll unravel the key symptoms, explore the various types, delve into the array of causes, and provide a comprehensive overview of current and emerging treatment options.

Symptoms of Hyposmia

The symptoms of hyposmia are often overlooked or attributed to other conditions, but recognizing them is essential for early intervention and management. People with hyposmia may notice changes that affect everyday experiences, from savoring meals to detecting dangerous odors. Understanding these symptoms helps individuals and clinicians identify the condition and seek appropriate care.

Symptom	Description	Impact	Sources
Reduced smell	Diminished ability to detect odors	Altered food enjoyment, safety concerns	2, 5
Altered taste	Food tastes bland or “off”	Decreased appetite, nutrition issues	10
Trouble identifying odors	Difficulty naming or distinguishing smells	Affects daily functioning and safety	2, 5
Emotional effects	Anxiety, frustration, or isolation	Quality of life impairment	2

Table 1: Key Symptoms

The Spectrum of Hyposmia Symptoms

Hyposmia can manifest in many ways, often subtle at first. The most common and defining symptom is a reduced ability to detect or recognize odors. Individuals might find that favorite foods seem bland, or that they miss environmental cues such as smoke or gas leaks, presenting safety risks 2, 5.

Impact on Taste and Nutrition

Because smell and taste are closely linked, many people with hyposmia report changes in how food tastes, sometimes leading to reduced appetite or difficulty maintaining proper nutrition 10. This can be especially pronounced in older adults or patients undergoing certain medical treatments.

Difficulties with Odor Identification

Beyond just a dulled sense of smell, many experience trouble naming or differentiating between odors. For example, distinguishing between the smell of coffee and chocolate may become challenging, affecting not just pleasure but also practical daily activities 2, 5.

Emotional and Social Implications

The inability to enjoy flavors or detect environmental hazards can lead to frustration, anxiety, or even social withdrawal—especially if the problem persists or worsens 2. Loss of smell has also been linked to cognitive decline in neurodegenerative conditions, further amplifying its impact.

Types of Hyposmia

Not all cases of hyposmia are the same. Understanding the different types helps in diagnosing the underlying cause and tailoring effective treatments. Hyposmia can be classified based on its origin, duration, and relationship to other conditions.

Type	Key Features	Typical Causes	Sources
Conductive	Obstruction blocks odor to receptors	Allergic rhinitis, polyps, sinusitis	1, 6
Sensorineural	Damage to olfactory nerves/epithelium	Neurodegenerative disease, viral infection, trauma	2, 4, 5
Mixed	Combination of both types	Chronic rhinosinusitis with nerve involvement	1
Transient	Temporary reduction in smell	Acute infections, medication effects	3, 10

Table 2: Hyposmia Types

Conductive Hyposmia

This type occurs when something physically blocks odor molecules from reaching the olfactory receptors in the nose. Common culprits include nasal congestion from allergies, chronic rhinosinusitis, or the presence of nasal polyps. The sense of smell often improves if the obstruction is removed 1, 6.

Sensorineural Hyposmia

Here, the problem lies in the sensory nerves or the olfactory epithelium itself. This can be due to damage from viral infections (like post-viral hyposmia), head trauma, or as an early symptom of neurodegenerative diseases like Parkinson’s or Alzheimer’s disease 2, 4, 5. Sensorineural hyposmia may be more persistent and less responsive to treatments aimed at reducing nasal obstruction.

Mixed Hyposmia

Some cases, especially in chronic conditions such as long-standing allergic rhinitis, involve both blockage and nerve dysfunction, creating a mixed clinical picture 1.

Transient Hyposmia

This form is temporary and often resolves once the underlying cause—such as a cold, flu, or medication effect—subsides. For example, some chemotherapy drugs (like 5-fluorouracil) can induce short-lived smell and taste disturbances 3, 10.

Causes of Hyposmia

Hyposmia has a wide range of causes, from localized nasal problems to systemic and neurological diseases. Identifying the underlying cause is crucial for selecting the most effective treatment and understanding the prognosis.

Cause	Description	Associated Conditions	Sources
Nasal/sinus disease	Inflammation or obstruction of nasal passages	Allergic rhinitis, sinusitis, nasal polyps	1, 6
Viral infections	Direct damage to olfactory epithelium	Post-viral hyposmia, COVID-19	3, 8
Neurodegenerative disorders	Central nervous system involvement	Parkinson’s, Alzheimer’s disease	2, 4, 5
Head trauma	Injury to olfactory nerves or bulbs	Post-traumatic hyposmia	5
Medications	Drug-induced olfactory dysfunction	Chemotherapy (5-FU), others	10
Idiopathic	Unknown cause	No clear association	3

Table 3: Common Causes

Nasal and Sinus Diseases

Chronic inflammation and physical blockages are leading causes of hyposmia worldwide. Allergic rhinitis is strongly associated with smell loss; studies show that nearly a quarter of patients with allergies may experience clinically significant hyposmia 1. The presence of sinusitis or nasal polyps further increases this risk.

Post-Viral and COVID-19 Hyposmia

Viral infections can directly damage the olfactory epithelium. This is particularly evident in post-viral hyposmia, which has become more recognized in the context of COVID-19. Many people report persistent smell loss weeks after mild COVID-19 infection, highlighting the virus’s unique impact on the olfactory system 3, 8.

Neurodegenerative Disorders

Hyposmia is a hallmark early symptom in diseases like Parkinson’s and Alzheimer’s. In Parkinson’s, changes in brain metabolism—particularly in areas like the piriform cortex and amygdala—lead to both olfactory and cognitive deficits 2, 5. In Alzheimer’s, amyloid-beta accumulation in the olfactory system can disrupt olfactory sensory neurons, contributing to early smell loss 4.

Trauma and Medications

Head injuries can directly damage the olfactory nerves, leading to sensorineural hyposmia that may be severe and persistent 5. Certain medications, such as topical and systemic chemotherapeutic agents like 5-fluorouracil, can also cause temporary smell disturbances 10.

Idiopathic Cases

In some instances, the cause remains unknown even after thorough investigation. These idiopathic cases require a broad diagnostic approach and may sometimes resolve spontaneously 3.

Treatment of Hyposmia

While hyposmia can be challenging to manage, a range of treatments are available and under investigation. The most effective approach depends on the underlying cause, duration, and severity of smell loss. New therapies and innovative methods are emerging to improve outcomes and patient adherence.

Treatment	Approach/Mechanism	Effectiveness	Sources
Olfactory training	Repetitive exposure to odors	Proven for various causes; better adherence with nasal inserts	9
Intranasal corticosteroids	Reduce inflammation in nasal passages	Effective in allergic/rhinitis-related hyposmia; limited in COVID-19	6, 8
Intranasal sodium citrate	Sequesters calcium, enhances transduction	Benefit in post-viral hyposmia	3
Intranasal insulin	Enhances olfactory nerve recovery	Promising early data	7
Treat underlying cause	Surgery, medication adjustment	Depends on etiology	1, 10

Table 4: Treatment Approaches

Olfactory Training

Olfactory training involves repeated exposure to a set of distinct odors, typically twice daily for several weeks. This non-invasive approach is supported by robust evidence and is recommended as first-line therapy for many types of hyposmia. Recent studies show that using scented nasal inserts can improve adherence and satisfaction, potentially leading to better outcomes 9. Training is most effective when started early and maintained consistently.

Intranasal Corticosteroids

For hyposmia linked to nasal inflammation—such as in allergic rhinitis or chronic sinusitis—intranasal steroids like betamethasone can significantly improve smell function 6. However, in cases of persistent COVID-19-related hyposmia, budesonide (another corticosteroid) did not show added benefit over saline alone, indicating a need for cause-specific treatment 8.

Intranasal Sodium Citrate

This therapy targets the chemical environment of the olfactory epithelium. Sodium citrate sequesters calcium, reducing feedback inhibition and potentially enhancing olfactory receptor sensitivity. It has demonstrated significant benefit in patients with post-viral hyposmia, providing a targeted option for this specific subgroup 3.

Intranasal Insulin

Emerging research suggests that delivering insulin intranasally may promote olfactory nerve recovery in some patients. Trials have shown significant improvements in smell scores compared to placebo, with no major adverse effects reported—though larger studies are needed to confirm these findings 7.

Addressing the Underlying Cause

When hyposmia results from a treatable underlying condition—such as nasal polyps, chronic rhinosinusitis, or medication side effects—targeted interventions (surgery, medication changes) may restore normal olfactory function 1, 10.

Conclusion

Hyposmia is a nuanced and multifaceted sensory disorder, often signaling broader health issues—from nasal inflammation to neurodegenerative disease. Early recognition of its symptoms and understanding the diverse causes and types are vital for effective management. While olfactory training stands out as a broadly effective therapy, new treatments are emerging, offering hope to those with persistent or severe smell loss.

Key Takeaways:

• Symptoms include reduced ability to smell, altered taste, and emotional impact 2, 5, 10.
• Types range from conductive and sensorineural to mixed and transient forms, each with distinct mechanisms 1, 2, 3, 4, 5, 6, 10.
• Causes are diverse, encompassing nasal diseases, viral infections (including COVID-19), neurodegenerative disorders, trauma, medications, and idiopathic origins 1, 2, 3, 4, 5, 6, 8, 10.
• Treatments include olfactory training (especially with nasal inserts for better adherence), intranasal steroids for inflammatory causes, sodium citrate for post-viral hyposmia, and emerging options like intranasal insulin 3, 6, 7, 8, 9.

Awareness, timely diagnosis, and a tailored treatment approach are the cornerstones of improving outcomes for individuals living with hyposmia.