Anosmia: Symptoms, Types, Causes and Treatment

Anosmia, the loss of the sense of smell, is a condition that many people become aware of only after experiencing it firsthand. Though it may seem like a minor inconvenience, anosmia can disrupt daily life, hinder safety, and even signal underlying health concerns. In the wake of the COVID-19 pandemic, anosmia has gained new attention as both a symptom and a research focus. This article explores anosmia's symptoms, types, causes, and available treatments—drawing from recent scientific studies and clinical experience.

Symptoms of Anosmia

Losing your sense of smell can be confusing and distressing. While some people notice it immediately, others may only realize it after failing to detect familiar odors, like coffee brewing or flowers blooming. Anosmia can occur alone or alongside other symptoms, such as taste disturbances or nasal congestion, and may arise suddenly or develop gradually.

Symptom	Frequency/Context	Associated Features	Source(s)
Loss of smell	Sudden or gradual	May be complete or partial	1 3 12
Loss of taste	Commonly co-occurring	Often with anosmia (ageusia)	1 3 12
Nasal symptoms	Sometimes present	Congestion, rhinorrhea	12 6
Isolated anosmia	Only symptom reported	Especially in COVID-19 cases	3 7 9
Quality of life	Mood, appetite changes	Safety risks (e.g., gas leaks)	12

Table 1: Key Symptoms Associated with Anosmia

Recognizing Anosmia

• Loss of Smell: The hallmark symptom is an inability to detect odors. Sometimes, this is total loss (anosmia); in other cases, there may be only a partial reduction (hyposmia) 1 12.
• Taste Disturbances: Because much of what we perceive as taste is actually smell, anosmia is often accompanied by a loss or alteration of taste (ageusia or dysgeusia) 1 3.
• Nasal and Sinus Symptoms: In some conditions, anosmia may arise together with nasal congestion, discharge, or other sinus issues. However, in certain cases (such as COVID-19), anosmia can appear without any nasal blockage 6 7 9.
• Isolated or Predominant Symptom: Notably, anosmia can sometimes be the only presenting symptom, especially in COVID-19, making it an important early warning sign 3 7 9.
• Impact on Daily Life: Anosmia can reduce appetite, blunt enjoyment of food and drink, and increase the risk of missing important environmental warnings—such as smoke or gas leaks 12.

Types of Anosmia

Anosmia isn't a one-size-fits-all diagnosis. Different forms exist, depending on timing, severity, and underlying mechanisms. Understanding these distinctions helps guide diagnosis and treatment.

Type	Description	Distinguishing Features	Source(s)
Congenital	Present from birth	Genetic or developmental causes	5 12
Acquired	Develops after birth	Injury, infection, or disease	5 12 14
Temporary	Reversible, short duration	Often due to infection or allergy	3 6 15
Permanent	Long-lasting or irreversible	Trauma, neurodegeneration	5 12 14

Table 2: Main Types of Anosmia

Congenital vs. Acquired Anosmia

• Congenital Anosmia: This form is present from birth, often due to genetic defects or developmental abnormalities in the olfactory system. Individuals may not realize what they are missing until later in life 5 12.
• Acquired Anosmia: More commonly, anosmia develops after birth due to a wide range of causes, including head injury, infections (such as viral upper respiratory infections), chronic sinus disease, or exposure to toxins 5 12 14.

Temporary vs. Permanent Anosmia

• Temporary Anosmia: Many cases are reversible, particularly those linked to temporary conditions like allergies, colds, or mild infections. Recovery is common, especially in younger patients or when the underlying cause is treatable 3 6 15.
• Permanent Anosmia: Some cases, such as those resulting from severe head trauma or neurodegenerative diseases, may be irreversible 5 12 14. In these situations, the loss of smell can be lifelong.

Other Variants

• Hyposmia: A partial reduction in the sense of smell.
• Parosmia: Distorted sense of smell.
• Phantosmia: Perception of odors that aren't present.

These variants can occur alone or in combination, sometimes complicating the clinical picture, especially following viral infections like COVID-19 4.

Causes of Anosmia

The list of possible causes for anosmia is long and varied. While some causes are temporary and benign, others may signal serious health issues.

Cause	Mechanism/Pathway	Notes	Source(s)
Viral infections	Damage to olfactory epithelium	e.g., COVID-19, influenza	1 2 3 7 8 10
Chronic sinus disease	Obstruction, inflammation	Often persistent	6 12
Head trauma	Injury to olfactory nerves/bulb	May be permanent	5 14
Neurodegenerative disease	Progressive neuronal loss	e.g., Parkinson's, Alzheimer's	12
Congenital defects	Developmental/genetic	Present from birth	5 12
Toxins/medications	Chemical injury	Smoking, certain drugs	12
Nasal polyps/tumors	Physical obstruction	May be treatable surgically	6 12
COVID-19 vaccination	Rare, transient cases reported	Usually resolves spontaneously	4

Table 3: Common Causes of Anosmia

Viral and Post-Infectious Anosmia

• COVID-19: Anosmia has become a defining and sometimes initial symptom of COVID-19. Unlike other respiratory viruses, COVID-19 can cause sudden anosmia even in the absence of nasal congestion 1 3 7 8 10. The virus appears to target the supporting cells (sustentacular cells) in the olfactory epithelium via the ACE2 receptor, leading to disruption of the olfactory system 8 9. In some cases, injury to the olfactory bulbs is visible on MRI, suggesting direct neural involvement 2.
• Other Viral Infections: Influenza and common cold viruses can also cause anosmia, typically due to inflammation and swelling that block odor detection 7 12.

Chronic Sinus Disease

• Obstructive Causes: Chronic sinusitis, nasal polyps, and other long-term inflammatory conditions can block airflow to the olfactory region, resulting in smell loss 6 12. Surgical intervention can help in some cases, but persistent mucosal disease is often associated with ongoing anosmia 6.

Trauma and Neurological Disorders

• Head Trauma: Blunt force injuries can shear the delicate olfactory nerves or damage the olfactory bulb, sometimes resulting in permanent anosmia 5 14.
• Neurodegenerative Diseases: Conditions like Parkinson’s and Alzheimer’s disease are frequently associated with progressive loss of smell, sometimes preceding other symptoms 12.

Other Causes

• Congenital Anomalies: Some people are born without a functional sense of smell due to developmental abnormalities 5 12.
• Chemical Exposure and Medications: Certain medications, toxins, or chronic smoking can damage olfactory receptors over time 12.
• COVID-19 Vaccination: Though rare, there are reports of temporary anosmia following COVID-19 vaccination, which generally resolve on their own 4.

Treatment of Anosmia

Treating anosmia depends on the underlying cause. While some cases resolve spontaneously, others require targeted interventions or ongoing management.

Treatment Approach	Application Context	Efficacy/Outcome	Source(s)
Address underlying cause	Infections, allergies	Often restores smell	6 12
Olfactory training	Viral/post-infectious	Safe, improves recovery	11 12
Topical corticosteroids	Sinusitis, allergies	Mixed evidence of benefit	11 13 15
Oral corticosteroids	Inflammatory causes	Sometimes helpful	13 14
Zinc supplementation	Traumatic anosmia	May improve outcomes	14
Surgery	Structural blockages	For polyps, tumors, etc.	6 12
Support/counseling	Permanent anosmia	Quality of life management	12

Table 4: Main Treatments for Anosmia

Treating the Underlying Cause

• Infections and Allergies: Treating sinus infections, allergies, or removing polyps can help restore smell in many cases 6 12.
• Surgical Options: When obstruction is the culprit, endoscopic sinus surgery may be considered, though not all patients regain full olfactory function 6.

Olfactory Training

• What Is It? Olfactory training involves regularly sniffing a set of distinct odors (e.g., rose, lemon, eucalyptus, clove) to stimulate recovery 11 12. It is safe and widely recommended for post-viral anosmia, including that caused by COVID-19 11.
• Effectiveness: While recovery rates vary, olfactory training can improve outcomes, especially when started early 11 12.

Medications

• Topical Corticosteroids: Used for inflammatory causes, but studies in post-COVID-19 anosmia show no significant benefit over olfactory training alone 11 15. Their role remains more established in chronic rhinosinusitis 13.
• Oral Corticosteroids: Sometimes used for inflammatory or autoimmune causes, but not routinely recommended for post-viral anosmia 13 14.
• Zinc Supplements: Some evidence supports their use in traumatic anosmia, though results are mixed 14.

Experimental and Supportive Therapies

• Emerging Approaches: Research is ongoing into treatments like tissue engineering, cell therapy, and smart drug delivery, particularly for long-term cases 10.
• Patient Support: Counseling and safety education are crucial for those with permanent anosmia, addressing risks related to food safety and environmental hazards 12.

Conclusion

Anosmia is a complex and sometimes underappreciated sensory disorder with a wide array of causes, types, and impacts on daily life. Whether it arises suddenly—as it often does with COVID-19—or develops gradually from chronic disease or trauma, anosmia deserves careful evaluation and management. Treatment success varies, but ongoing research and increased awareness offer hope for more effective solutions in the future.

Key Takeaways:

• Anosmia involves partial or complete loss of smell and can significantly affect quality of life.
• Types include congenital, acquired, temporary, and permanent forms, each with unique causes and implications.
• Leading causes range from viral infections (notably COVID-19) and chronic sinus disease to head trauma and neurodegenerative conditions.
• Treatment is tailored to the cause, with olfactory training and treating underlying conditions as mainstays; medications and surgery are sometimes appropriate.
• Support and education are essential for those living with permanent anosmia.

By understanding anosmia more deeply, patients and clinicians alike can better recognize, diagnose, and address this impactful condition.