Anosmia: Symptoms, Causes and Treatment

Anosmia—the complete loss of the sense of smell—has surged into public awareness, especially in the wake of the COVID-19 pandemic. While it might sound like a minor inconvenience, anosmia can profoundly affect safety, nutrition, mood, and overall quality of life. Understanding its symptoms, causes, and treatment options is crucial not just for those experiencing it, but also for healthcare providers and the broader public. This article offers a comprehensive guide to anosmia, drawing from the latest research and clinical insights.

Symptoms of Anosmia

Losing your sense of smell can be disorienting, isolating, and sometimes dangerous. For some, anosmia comes on suddenly; for others, it develops gradually. Recognizing the key symptoms is vital for early detection and management.

Symptom	Description	Associated Features	Source(s)
Loss of smell	Total inability to perceive odors	May be sudden or gradual	1 3 6 11
Loss of taste	Diminished or altered sense of taste	Often co-occurs with anosmia	1 3 4 14
Parosmia	Distorted perception of odors	Sometimes follows anosmia recovery	4 8
Phantosmia	Perception of smells that aren’t present	Less common, can be distressing	4
Fatigue	General tiredness	Frequently reported with anosmia	3
Headache	Persistent or recurrent headaches	Sometimes co-occurs with anosmia	2 4
Cough	Dry or productive cough	Especially in COVID-19 cases	3

Table 1: Key Symptoms of Anosmia

Sudden vs. Gradual Loss of Smell

Anosmia can present abruptly, especially in cases related to viral infections such as COVID-19, or it may develop over time due to chronic conditions. Sudden onset is frequently reported in COVID-19, often without accompanying nasal congestion or rhinitis, making it a distinctive symptom compared to other respiratory illnesses 1 6. In chronic sinus disease or after head trauma, the loss of smell is more likely to develop progressively 5 13.

Associated Symptoms: Taste Disturbances and Beyond

A striking feature of anosmia, particularly in COVID-19 cases, is the concurrent loss or alteration of taste—known as ageusia or dysgeusia 1 3 4 14. In children and adults alike, the overlap between smell and taste loss can be so pronounced that individuals often report food as “tasteless” or “bland” 3. Additional symptoms such as fatigue, cough, and headache frequently accompany anosmia in infectious contexts 2 3.

Variants of Olfactory Dysfunction

Not all olfactory disorders are the same. Some patients experience parosmia (distorted smells) or phantosmia (perceiving odors that aren’t present), especially during the recovery phase from viral-induced anosmia 4 8. These can be distressing but are usually transient.

Impact on Daily Life

The inability to detect warning odors—like smoke or spoiled food—poses safety risks. Moreover, anosmia can lead to reduced appetite, weight loss, and even depression due to the loss of pleasure from eating and social interactions 11.

Causes of Anosmia

The origins of anosmia are broad and complex, spanning temporary blockages to irreversible neural damage. Understanding these causes is key to effective diagnosis and management.

Cause	Mechanism	Typical Onset	Source(s)
Viral infections	Damage to olfactory epithelium/cells	Sudden	1 6 7 8 9
Chronic sinusitis	Mucosal inflammation, polyp formation	Gradual	5
Head trauma	Direct injury to olfactory nerves/bulbs	Sudden	2 13
Neurodegenerative diseases	Loss of olfactory neurons	Progressive	11
COVID-19	Direct/indirect viral injury to olfactory system	Sudden	1 2 3 6 7 8 9
Vaccination	Possible immune-related temporary changes	Acute (rare)	4

Table 2: Primary Causes of Anosmia

Viral Infections

Viruses are a leading cause of sudden anosmia. COVID-19, in particular, is strongly associated with abrupt loss of smell, often as an early or even sole symptom 1 3 6 7 8 9. The mechanism involves the virus targeting non-neuronal supporting cells (sustentacular cells) in the olfactory epithelium, which express high levels of ACE2 and TMPRSS2 receptors—the viral entry points 7 8 9. This indirect damage can disrupt olfactory neuron function.

Other viruses, including those causing the common cold and influenza, can also trigger temporary anosmia through nasal inflammation and mucosal swelling 6 7.

Chronic Sinus Disease

Chronic rhinosinusitis is a common non-infectious cause. Persistent inflammation, mucosal thickening, and nasal polyps can block odor molecules from reaching the olfactory epithelium, leading to conductive anosmia 5. Even after surgical intervention, many patients continue to experience reduced or absent smell if underlying mucosal disease persists 5.

Head Trauma

Traumatic injury—ranging from mild concussion to severe head trauma—can shear olfactory nerve fibers or damage the olfactory bulbs, resulting in sudden and sometimes permanent anosmia 2 13. Recovery is variable and often incomplete.

Neurodegenerative Disorders

Conditions such as Parkinson’s disease and Alzheimer’s disease may feature gradual loss of smell as an early sign, reflecting degeneration of olfactory neurons 11. Olfactory testing is sometimes used as a screening tool in these populations.

COVID-19 Vaccination

While rare, some individuals have reported transient anosmia or related symptoms following COVID-19 vaccination. These events are usually self-limiting and resolve without intervention 4.

Other Contributing Factors

• Aging: Olfactory function declines with age, with prevalence of anosmia increasing significantly in older adults 11.
• Congenital factors: Some individuals are born without a sense of smell (congenital anosmia), usually due to genetic mutations 11.

Treatment of Anosmia

Treating anosmia hinges on addressing its underlying cause, but options remain limited, especially for neural damage. Recent research offers hope, yet full recovery is not always possible.

Treatment	Approach/Mechanism	Effectiveness	Source(s)
Olfactory training	Repeated exposure to specific odors	Moderate improvement	10 11
Corticosteroid sprays	Reduce inflammation in nasal passages	Mixed evidence	10 12 14
Systemic steroids	Treat underlying inflammation	Modest benefit (select cases)	12 13
Zinc supplementation	Supports neural repair (in trauma)	Promising in traumatic cases	13
Surgical intervention	Remove obstructions (e.g., polyps)	Variable; depends on cause	5 11
Spontaneous recovery	Natural resolution over time	Common in viral cases	3 4 14
Advanced therapies	Cell therapy, tissue engineering (experimental)	Under investigation	9

Table 3: Treatment Approaches for Anosmia

Olfactory Training: A First-Line Strategy

Repeated, structured exposure to a set of odors—known as olfactory training—can help stimulate recovery, especially in post-viral cases 10 11. This approach is non-invasive, safe, and supported by moderate evidence. Patients are encouraged to sniff distinct scents (like rose, lemon, eucalyptus, and clove) for several minutes daily over weeks or months.

Corticosteroids: Mixed Results

Topical nasal corticosteroids, such as mometasone or betamethasone, are commonly prescribed to reduce nasal inflammation. However, research in COVID-19-associated anosmia has not shown significant benefits over olfactory training alone 10 14. Systemic corticosteroids may offer modest improvement in select cases, such as inflammatory sinus disease or post-traumatic anosmia, but potential side effects must be considered 12 13.

Zinc Supplementation

Zinc plays a role in neural repair and regeneration. In cases of traumatic anosmia, zinc gluconate—alone or combined with steroids—has shown promising results in restoring some olfactory function 13. Its role in post-viral anosmia remains less clear.

Surgical Options

For anosmia caused by physical obstruction (e.g., chronic sinusitis with polyps), endoscopic sinus surgery can restore airflow and improve smell in many patients. However, success rates vary, and persistent mucosal disease may limit recovery 5 11.

Spontaneous Recovery and Prognosis

Many individuals, especially with viral-induced anosmia, experience spontaneous recovery within weeks to months 3 4 14. In a large pediatric study, 83% of COVID-19 patients recovered their sense of smell within 30 days, with a median recovery time of about 13 days 14. However, a subset of patients—particularly those with more severe initial loss or prolonged symptoms—may face persistent deficits 3 14.

Emerging and Experimental Therapies

Research into advanced therapies—such as tissue engineering, cell therapy, and smart drug delivery—offers hope for those with long-term or intractable anosmia 9. While these approaches remain experimental, they highlight the importance of ongoing research and innovation.

Patient Counseling and Safety

Given the risks associated with anosmia (e.g., inability to smell smoke, gas leaks, or spoiled food), patient education is essential. Practical advice includes installing smoke detectors, checking food expiration dates, and maintaining good kitchen hygiene 11.

Conclusion

Anosmia is more than just a loss of smell—it's a condition that touches safety, nutrition, social life, and emotional well-being. The COVID-19 pandemic has brought this often-overlooked disorder into the spotlight, highlighting both its prevalence and its profound impact.

Key Takeaways:

• Symptoms: Sudden or gradual loss of smell is often accompanied by taste disturbances, fatigue, and sometimes headaches or cough. Variants include parosmia and phantosmia.
• Causes: Most commonly due to viral infections (especially COVID-19), chronic sinus disease, head trauma, or neurodegenerative disorders. Rarely, vaccination or congenital factors may play a role.
• Treatment: Olfactory training is the mainstay for most, with limited evidence supporting the routine use of corticosteroids. Zinc may help in traumatic cases. Many cases recover spontaneously, but persistent anosmia requires ongoing research and support.
• Patient Safety: Individuals with anosmia should be counseled on safety measures and coping strategies to maintain quality of life.

The evolving scientific understanding of anosmia underscores the need for continued research, comprehensive care, and compassionate support for those affected.