What Is Anosmia?
Anosmia is the complete loss of olfactory capacity, while hyposmia refers to a partial reduction of smell. It is a chemosensory dysfunction that significantly affects quality of life, food safety, and emotional well-being.
Olfactory dysfunction affects 3% to 20% of the general population, rising with age. The COVID-19 pandemic put anosmia in the spotlight, since up to 85% of infected patients experienced some degree of smell loss during the acute phase.
Beyond robbing patients of food enjoyment, anosmia compromises their ability to detect environmental hazards such as gas leaks and spoiled food. Studies link chronic anosmia to increased depressive symptoms, social isolation, and reduced caloric intake, especially in older adults.
Olfactory Neuroepithelium
Olfactory neurons are the only neurons of the central nervous system directly exposed to the environment, making them vulnerable to viruses, toxins, and trauma.
Impact on Quality of Life
Anosmia affects taste (80% of flavor depends on smell), food safety, and emotional well-being, with elevated rates of associated depression.
Regenerative Capacity
The olfactory epithelium can regenerate neurons throughout life, which underpins recovery potential even after prolonged loss.
Pathophysiology
Smell depends on the olfactory neuroepithelium, located in the roof of the nasal cavity. Bipolar olfactory neurons have cilia that contain specific receptors for odor molecules. Each neuron expresses a single receptor type, and signals are transmitted by the olfactory nerve (cranial nerve I) to the olfactory bulb.
Anosmia can be classified into three categories: conductive (obstruction of nasal airflow), sensorineural (lesion of the neuroepithelium or olfactory nerve), and central (lesion of the olfactory bulb or córtex). The conductive cause is the most common and is generally reversible.
Post-Viral Mechanism
Upper airway viral infections are the second most common cause of anosmia. Viruses directly damage olfactory neurons and the supporting cells of the neuroepithelium. SARS-CoV-2 predominantly infects supporting cells via the ACE2 receptor, inflaming and disrupting the neuronal microenvironment.
Recovery depends on olfactory neurons regenerating from progenitor basal cells. This process can take weeks to months and, in some cases, regeneration is incomplete or aberrant, resulting in parosmia (distortion of odors) or phantosmia (perception of phantom odors).
Symptoms
Clinical presentation varies with the degree of olfactory loss. Patients often perceive total anosmia as loss of taste, since flavor perception depends largely on retronasal olfaction. Hyposmia can be insidious and is often underdiagnosed.
Manifestations of Anosmia
- 01
Complete or partial loss of smell
Inability to perceive environmental odors, perfumes, foods, or hazardous substances such as gas and smoke.
- 02
Loss of food flavor
Main complaint in many patients. Basic taste (sweet, salty, sour, bitter) is preserved, but complex flavors are lost.
- 03
Parosmia
Qualitative distortion of odors — familiar smells become unpleasant. Common during the post-viral recovery phase.
- 04
Phantosmia
Perceiving odors with no real stimulus present. Usually unpleasant (cacosmia). May indicate a central cause.
- 05
Reduced appetite and weight loss
Losing enjoyment of food reduces caloric intake, especially in older adults.
- 06
Depressive symptoms and anxiety
Smell is closely linked to emotions via the limbic system. Chronic anosmia is associated with elevated rates of depression.
- 07
Safety concerns
Inability to detect gas leaks, smoke, spoiled food, and hazardous chemicals.
Diagnosis
Diagnosing anosmia requires a systematic evaluation including a detailed history, a complete otolaryngologic examination, and standardized olfactory tests. Nasal endoscopy is fundamental for assessing nasal anatomy and identifying conductive causes.
Magnetic resonance imaging is indicated to assess the olfactory bulb (reduced volume correlates with poor prognosis), exclude intracranial lesions, and investigate central causes. Computed tomography of the paranasal sinuses is useful for evaluating chronic rhinosinusitis and nasal polyposis.
🏥Diagnostic Evaluation of Anosmia
- 1.Detailed history: sudden vs. gradual onset, relationship with URTI, trauma, surgery, or medications
- 2.Nasal endoscopy: assesses mucosa, septum, turbinates, and any polyps or masses
- 3.Olfactory tests: Sniffin Sticks or UPSIT to objectively quantify the déficit
- 4.Magnetic resonance imaging: olfactory bulb volume, intracranial lesions, neurodegeneration
- 5.Computed tomography of paranasal sinuses: evaluates chronic rhinosinusitis and nasal polyposis
DIFFERENTIAL DIAGNOSIS
Differential Diagnosis
Chronic Rhinosinusitis
- Bilateral nasal obstruction
- Purulent rhinorrhea
- Facial pressure
- Associated nasal polyposis
Diagnostic Tests
- CT of paranasal sinuses
- Nasal endoscopy
- Olfactory test (Sniffin Sticks)
Acupuncture may reduce nasal inflammation and improve airway patency as an adjuvant.
Parkinson Disease (early hyposmia)
- Hyposmia precedes tremor by years
- Postural instability
- Bradykinesia
- Constipation and vivid dreams
- Isolated hyposmia in a patient over 60 warrants a neurodegenerative workup
Diagnostic Tests
- DaTscan (dopaminergic SPECT)
- Neurological evaluation
- Brain MRI
Post-acute COVID-19 (Long COVID)
- Persistent hyposmia/parosmia > 12 weeks
- Fatigue
- Brain fog
- History of SARS-CoV-2 infection
Diagnostic Tests
- Quantified olfactory test
- MRI of olfactory bulb
- Post-COVID symptom questionnaire
Acupuncture combined with olfactory training has shown benefit in studies of post-COVID anosmia.
Olfactory Meningioma
- Progressive unilateral anosmia
- Frontal headache
- Personality changes
- Unilateral exophthalmos
- Progressive unilateral anosmia is a red flag — requires urgent neuroimaging
Diagnostic Tests
- Brain MRI with gadolinium
- CT of skull base
Kallmann Syndrome
- Congenital anosmia
- Hypogonadotropic hypogonadism
- Onset at puberty
- No sexual development
Diagnostic Tests
- FSH, LH, testosterone/estradiol
- MRI (absent olfactory bulbs)
- Karyotype
Post-Viral Anosmia vs. Chronic Rhinosinusitis
The most common differential in practice is between post-viral anosmia and chronic rhinosinusitis. In post-viral cases, onset is sudden — often after a URTI — without prominent nasal obstruction, and the olfactory loss is disproportionate to inflammation. Chronic rhinosinusitis presents with nasal obstruction, rhinorrhea, and sinus opacification on imaging. Nasal endoscopy and CT of the paranasal sinuses settle the distinction.
In prolonged post-COVID anosmia (> 12 weeks), MRI may show reduced olfactory bulb volume, correlating with poorer prognosis. Structured olfactory training, started early, remains the intervention with the best evidence.
Red Flags in the Diagnosis of Anosmia
Progressive unilateral anosmia, especially with headache or visual changes, requires immediate neuroimaging to rule out an olfactory groove meningioma or other skull base lesion. Consider Kallmann syndrome in young patients with congenital anosmia and absent pubertal development — early diagnosis allows hormonal treatment and preserves fertility.
Hyposmia in patients over 60, even when isolated, can precede a Parkinson disease diagnosis by years — the PREDICT-PD study documents hyposmia as an early biomarker. The medical acupuncturist should watch for these warning signs in the history.
Kallmann Syndrome and Congenital Causes
Kallmann syndrome is a rare congenital cause of anosmia, characterized by bilateral absence or hypoplasia of the olfactory bulbs together with hypogonadotropic hypogonadism. The genetic defect (mutations in KAL1, FGFR1, PROKR2, among others) disrupts the embryonic migration of olfactory neurons and GnRH-producing neurons. Diagnosis is clinical and genetic, confirmed by absent olfactory bulbs on brain MRI and by low FSH, LH, and testosterone or estradiol, depending on sex. Hormone replacement therapy enables pubertal development and, in many cases, assisted fertility.
Distinguishing Kallmann syndrome from acquired anosmia (post-viral, post-traumatic) is essential, since management differs substantially. Acupuncture has a limited role in Kallmann syndrome, since the absent olfactory neuroepithelium does not respond to conventional olfactory training. However, acupuncture may help support general well-being and secondary symptoms such as depression tied to the diagnosis. The medical acupuncturist should recognize this presentation and refer appropriately to an endocrinologist.
Treatment
Treating anosmia depends on the underlying cause. Conductive causes (polyposis, rhinosinusitis) respond to treating the underlying disease. For sensorineural anosmia, olfactory training is the intervention with the best evidence and may be combined with other approaches.
Treatment of the Conductive Cause
Nasal and systemic corticosteroids for nasal polyposis. Saline nasal lavage. Endoscopic nasal surgery (polypectomy, septoplasty) when indicated. Treat any underlying chronic rhinosinusitis.
Olfactory Training
Repeated and conscious exposure to four intense odors (rose, eucalyptus, lemon, clove) for 20 seconds each, twice daily, for at least 12 weeks. Level A evidence for post-viral anosmia.
Adjuvant Pharmacotherapy
Short courses of oral corticosteroids for inflammatory anosmia. Omega-3 and topical nasal vitamin A remain under investigation. Intranasal sodium citrate for parosmia. No evidence supports routine vitamins or supplements.
Complementary Therapies
Acupuncture as an adjuvant to olfactory training. Psychological support for the emotional toll of chronic anosmia. Guidance on food and home safety.
Acupuncture as Treatment
Acupuncture has been investigated as a complementary therapy for anosmia, with proposed mechanisms that include possible increase of blood flow in the nasal mucosa, modulation of local neuroinflammation, stimulation of olfactory neurogenesis, and regulation of the nasal autonomic nervous system. These are hypotheses based on experimental studies that still need to be confirmed in more robust clinical trials.
Clinical studies suggest that acupuncture combined with olfactory training may help olfactory function recover in patients with post-viral anosmia, though the evidence base is limited. Points such as Yingxiang (LI20), Bitong (extra), Yintang (extra), and Hegu (LI4) appear frequently in described protocols.
Stimulating perinasal points may promote local vasodilation, according to experimental studies. Acupuncture may also modulate inflammatory cytokines (such as IL-6 and TNF-alpha), which could favor a microenvironment conducive to neuronal regeneration — a mechanistic hypothesis that does not equate to proven clinical efficacy.
Prognosis
Anosmia prognosis depends fundamentally on the cause. Conductive anosmia from polyposis or rhinosinusitis carries a good prognosis with appropriate treatment. Post-viral anosmia recovers spontaneously in 60-80% of cases within 12-18 months, though recovery may be incomplete.
Post-traumatic anosmia carries a more reserved prognosis, with recovery in only 10-30% of cases, depending on trauma severity. Anosmia tied to neurodegenerative disease (Parkinson, Alzheimer) tends to be progressive and irreversible.
Favorable prognostic factors include: recent onset, an identifiable and treatable cause, preserved olfactory bulb volume on MRI, and parosmia during recovery (indicates active neuronal regeneration). Adherence to olfactory training is decisive for long-term outcomes.
Myths and Facts
Myth vs. Fact
Losing smell is inconvenient but not serious
Anosmia compromises safety (detecting gas, smoke, spoiled food), nutrition, and mental health. It carries significant depression rates and can be an early symptom of neurodegenerative disease.
Post-COVID anosmia always resolves on its own
Although most recover, 5-10% of patients still have significant olfactory dysfunction at 12 months. Starting olfactory training early improves recovery rates.
There is no treatment for anosmia
Olfactory training has level A evidence. Conductive causes are treatable. Acupuncture, corticosteroids, and other approaches can be combined based on etiology.
Parosmia means something is getting worse
Parosmia usually signals active neuronal regeneration — new neurons are reconnecting, just imperfectly. It is a sign of ongoing recovery.
When to Seek Help
A specialist should evaluate olfactory loss when it is persistent, suddenly onset without an apparent cause, or accompanied by other neurological symptoms.
Frequently Asked Questions about Anosmia
Most patients recover their sense of smell within 3-6 months. About 5-10% still have significant olfactory dysfunction at 12 months. Starting olfactory training early and adding acupuncture as an adjuvant improve recovery rates.
Yes. Olfactory training has level A evidence for post-viral anosmia. The protocol: smell four intense odors (rose, eucalyptus, lemon, clove) for 20 seconds each, twice daily, for at least 12 weeks. The mechanism is stimulating olfactory neurons to regenerate and reconnect.
Parosmia is a qualitative distortion of odors — familiar smells become unpleasant, often described as garbage, sewage, or burnt. Despite the discomfort, parosmia usually signals active neuronal regeneration and is a sign of ongoing recovery.
Yes, in some cases. Progressive unilateral anosmia may indicate an olfactory groove meningioma. Hyposmia in older adults can precede Parkinson disease. Congenital anosmia with hypogonadism suggests Kallmann syndrome. For this reason, any persistent anosmia, or any anosmia not linked to a URTI, warrants medical evaluation.
Acupuncture acts through several mechanisms: increasing blood flow in the nasal mucosa, modulating local neuroinflammation, stimulating olfactory neurogenesis, and regulating the nasal autonomic nervous system. Points such as Yingxiang (LI20), Bitong, and Yintang are commonly used. The medical acupuncturist tailors the protocol to each patient.
Most of the time, yes. When the nose gets blocked during a cold, retronasal olfaction is impaired and flavor perception drops sharply, though basic taste (sweet, salty, sour, bitter) is preserved. This is temporary conductive anosmia, distinct from post-viral sensorineural anosmia.
Evidence is limited for most supplements. Omega-3 and topical nasal vitamin A remain under investigation. Intranasal sodium citrate may help with parosmia. Zinc may help when deficiency is documented. Routine supplementation is not recommended without a prior medical evaluation.
Significantly. Patients with anosmia cannot detect gas leaks, fire smoke, spoiled food, or chemicals. We recommend installing gas and smoke detectors at home, checking food expiration dates visually, and adapting safety routines accordingly.
Yes. Smell is the sense most closely tied to emotions and memories through the limbic system. Chronic anosmia carries elevated rates of depression, anxiety, social isolation, and reduced quality of life. Integrating psychological support into anosmia treatment is an important part of care.
Refer when: olfactory loss persists more than 2 weeks after a viral infection; onset is sudden without a prior URTI; the loss is unilateral; it comes with headache or visual or neurological changes; or parosmia/phantosmia is disabling. The medical acupuncturist can begin complementary treatment in parallel with specialist workup.
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