Parosmia: Symptoms, Types, Causes and Treatment

Parosmia—a condition where familiar smells become distorted, often unpleasant or even revolting—has come into the spotlight, especially since the COVID-19 pandemic. This complex olfactory disorder impacts not just the sense of smell, but also quality of life and mental well-being. In this article, we dive deep into the symptoms, types, causes, and treatment options for parosmia, synthesizing the latest scientific research and patient experiences.

Symptoms of Parosmia

Parosmia can be a distressing experience, turning daily pleasures like the aroma of coffee or favorite foods into sources of disgust or nausea. Recognizing its symptoms is the first step in understanding and managing this condition.

Symptom	Description	Impact	Sources
Distorted Smell	Familiar odors smell unpleasant or strange	Triggers disgust, aversion, or nausea	1 2 3 10
Triggered by Odor	Distortion happens only in presence of odor	Common triggers: coffee, meat, onion, toothpaste	2 3 12
Emotional Distress	Anxiety, depression, reduced quality of life	Social isolation, mental health impact	1 3 4 12
Associated Taste Changes	Food tastes off or unpalatable	Loss of appetite, weight changes	1 10 12

Table 1: Key Symptoms

Understanding the Symptoms

Distorted and Unpleasant Odors

• Parosmia is defined by the distortion of smells in the presence of an odorant—meaning, actual smells are present, but they are perceived as altered or foul, often described as burnt, chemical, sewage-like, or rotten 1 2 3 10.
• Coffee, meat, onions, toothpaste, and other everyday items are frequently reported as triggers 2 3 12.
• The experience is almost universally unpleasant and can provoke strong aversive reactions 1 2 3.

Triggers and Variability

• Not all odors cause parosmia; certain molecules, especially those with strong or distinctive smells, are more likely to be triggers 2 8.
• Symptoms can fluctuate in intensity and duration, and patients may have periods of improvement followed by relapse 3.

Emotional and Mental Health Consequences

• The condition significantly affects mental health, leading to anxiety, depression, and a sense of isolation 1 3 4 12.
• More than half of patients in some studies reported severe impacts on quality of life 1 12.

Associated Taste Changes

• Since smell is closely tied to taste, many individuals with parosmia also report dysgeusia (distorted taste) or loss of appetite 1 10 12.
• Food becomes "almost unpalatable," which can lead to weight loss or nutritional issues 10 12.

Types of Parosmia

Parosmia is not a one-size-fits-all condition. Understanding its different types helps tailor diagnosis and management.

Type	Characteristic Feature	Prevalence/Notes	Sources
Classic Parosmia	Unpleasant distortion of familiar odors	Most common type	1 2 3 6
Euosmia	Pleasant distortion (rare)	Exceptionally rare	6
Troposmia	Parosmia with specific aversive responses	Often post-infectious	12
Mixed Qualitative Disorders	Parosmia plus phantosmia (hallucinated smells)	Co-occurrence is common	3 4 5

Table 2: Types of Parosmia

Breaking Down the Types

Classic Parosmia

• The majority of parosmia cases are characterized by unpleasant, often disgusting distortions of familiar odors 1 2 3.
• Triggers are typically common foods and scents, with a strong emotional and behavioral aversion as a hallmark 2 3.

Euosmia: A Rare Exception

• Euosmia refers to a rare form of parosmia where the distortion is actually perceived as pleasant rather than foul 6.
• Documented only in isolated cases, euosmia highlights the complexity and subjectivity of olfactory processing 6.

Troposmia

• Troposmia describes parosmia where specific odors (often those from certain food or environmental sources) reliably trigger aversive or negative reactions 12.
• This term is gaining traction, especially in the context of post-viral parosmia.

Mixed Qualitative Disorders

• Many individuals with parosmia also experience phantosmia—the perception of smells that aren't present (olfactory hallucinations) 3 4 5.
• This overlap can complicate diagnosis and treatment, as the conditions may fluctuate or co-occur.

Causes of Parosmia

Parosmia is a symptom, not a disease, arising from a range of underlying causes. Recent research has shed light on both triggers and mechanisms.

Cause	Main Mechanism/Trigger	Context/Notes	Sources
Post-viral (COVID-19, flu)	Olfactory nerve injury/regeneration	Most common since pandemic	1 5 10 12
Traumatic Brain Injury	Damage to olfactory pathways	Often with hyposmia/anosmia	1 4 6 14
Sinonasal Disease	Obstruction, inflammation	Includes chronic rhinosinusitis	4 9 14
Toxins/Drugs	Direct neurotoxicity	Includes some antibiotics	14
Neurological Disorders	Central processing abnormalities	Rare, includes tumors, epilepsy	6 9
Idiopathic	Unknown	1/3 of cases	4

Table 3: Causes of Parosmia

Exploring the Causes

Post-Infectious Parosmia

• The most common cause is viral infection, especially COVID-19, but also influenza and other upper respiratory viruses 1 5 10 12.
• Parosmia often emerges during recovery from anosmia (complete loss of smell) or hyposmia (partial loss), as olfactory neurons regenerate 1 10 12.

Pathophysiology: Miswiring and Molecular Triggers

• The leading hypothesis is that regenerating olfactory sensory neurons may "miswire" or reconnect incorrectly after injury, leading to distorted brain signals and faulty odor perception 2 8 10.
• Some research shows that specific highly odor-active molecules (such as certain thiols and pyrazines in coffee) can trigger parosmia, suggesting a receptor-level phenomenon as well 2 8 9.
• The process is thought to be a mix of peripheral (olfactory nerve) and central (brain processing) dysfunction 8 10.

Other Causes

• Head injury, sinonasal disease (such as chronic sinusitis), toxic exposures, and certain medications (notably some antibiotics) can all damage olfactory pathways and lead to parosmia 4 6 9 14.
• Neurological conditions, including epilepsy, brain tumors, and psychiatric disorders, are rare but documented causes 6 9.
• In up to a third of cases, no clear cause is identified (idiopathic parosmia) 4.

COVID-19 and the Surge in Parosmia

• Since the COVID-19 pandemic, there has been a dramatic increase in parosmia cases, often in younger, otherwise healthy individuals 5 10 12.
• Parosmia is now recognized as a common feature of "long COVID" and can persist for months or even longer 10 12.

Treatment of Parosmia

Managing parosmia can be challenging, as there is no universal cure. However, a combination of therapies and supportive strategies can help alleviate symptoms and improve quality of life.

Treatment Approach	Description/Method	Effectiveness/Notes	Sources
Olfactory Training (OT)	Repeated exposure to selected odors	Most evidence-based, especially for post-viral parosmia	9 10 11 15
Modified OT (MOT)	Extended/more varied odor training	Effective for COVID-19 parosmia	9 11
Medications	Gabapentin, pregabalin, sodium valproate	Used in select cases, limited evidence	7 9
Supplements	Omega-3, vitamin B12, zinc	Often tried, effectiveness unclear	13 15
Platelet-Rich Plasma (PRP)	Injections into olfactory cleft	Promising for refractory cases	13
Supportive Care	Counseling, support groups, coping strategies	Important for mental well-being	3 4 9

Table 4: Parosmia Treatments

Treatment Strategies Explained

Olfactory Training (OT) and Modified OT

• OT involves the structured, repeated smelling of specific odorants (commonly lemon, rose, clove, and eucalyptus) twice daily for months 10 11.
• Modified OT (MOT) uses a broader array of scents and longer duration, showing improved outcomes, particularly for COVID-19-induced parosmia 9 11.
• Studies report significant improvements in olfactory function and symptom reduction with consistent practice 9 11 15.

Pharmacological Therapies

• Medications such as gabapentin, pregabalin, and sodium valproate have been used off-label, but evidence is limited and potential side effects must be considered (especially for sodium valproate in women of childbearing age) 7 9.
• Other drugs, including corticosteroids and anti-inflammatories, may be tried, particularly if underlying inflammation is suspected, but long-term benefits are uncertain 13 15.

Nutritional Supplements

• Omega-3 fatty acids, vitamin B12, and zinc supplementation are often recommended, especially if deficiencies are suspected, but their efficacy for parosmia specifically remains under investigation 13 15.

Platelet-Rich Plasma (PRP) Therapy

• PRP involves injecting concentrated platelets from the patient’s own blood into the olfactory cleft. Early studies suggest benefit in some patients who failed other treatments 13.
• While promising, PRP remains experimental and is not widely available.

Support and Coping Strategies

• Psychological support, counseling, and participation in patient support groups are vital, given the profound impact on mental health and daily life 3 4 9.
• Patients may also benefit from practical coping strategies, such as avoiding triggers, modifying diet, and using flavor enhancers to compensate for taste loss 4.

Prognosis and Expectations

• Recovery from parosmia is often gradual and may take months or even years 1 10 12.
• In some cases, spontaneous improvement occurs, and the onset of parosmia after anosmia can be a sign of ongoing neural recovery 10.
• Despite advances, many patients experience persistent symptoms and ongoing challenges 12 15.

Conclusion

Parosmia is an often misunderstood yet profoundly impactful condition. The surge in cases following COVID-19 has brought new attention to its symptoms, mechanisms, and treatments. While science has made progress in identifying triggers and understanding the underlying biology, effective management remains a work in progress.

Key takeaways:

• Symptoms: Parosmia causes distorted, usually unpleasant smells, triggered by familiar odors, with significant impacts on taste, appetite, and mental health 1 2 3 10 12.
• Types: Most cases are classic (unpleasant), but rare forms like euosmia (pleasant distortion) exist. Parosmia often overlaps with other olfactory disorders like phantosmia 3 4 6.
• Causes: The main cause is post-infectious (especially COVID-19), but trauma, sinonasal disease, toxins, neurological disorders, and idiopathic cases also occur 1 4 5 6 10 12 14.
• Treatment: Olfactory training is the cornerstone of therapy, with modified protocols showing promise. Medications, supplements, and experimental options like PRP may help some patients. Psychological support is essential due to the condition’s impact on quality of life 9 10 11 13 15.

For those living with parosmia, hope lies in emerging therapies, ongoing research, and a growing recognition of the condition’s challenges—ensuring that patients are heard, supported, and empowered through their recovery journey.