What are the main causes of loss of taste in adults, particularly older adults?

Main Causes of Loss of Taste in Adults

Loss of taste in adults is most commonly caused by viral upper respiratory infections—particularly COVID-19, which affects 59-86% of infected patients—followed by age-related physiological decline, medications (especially anticholinergics), chronic rhinosinusitis, neurological diseases, and head trauma. 1

Viral Infections (Most Common Acute Cause)

COVID-19 is the predominant viral cause, affecting taste/smell in 59-86% of infected patients, with loss presenting as the initial or sole symptom in 11.9-22% of cases. 1, 2 The key clinical distinction is that traditional nasal symptoms (congestion, rhinorrhea) are typically absent with COVID-19-related taste loss, unlike other viral infections. 2

• Post-viral olfactory loss accounts for approximately 11% of community cases and 20-25% of specialist clinic presentations, with coronaviruses being well-established culprits. 1
• Recovery occurs in 73% of patients within 7-14 days, though 20% have symptoms persisting beyond 14 days, and some experience permanent dysfunction. 2
• Critical pitfall: Most "taste loss" in viral infections actually reflects loss of retronasal olfaction (flavor perception) rather than true taste dysfunction, since true taste only differentiates sweet, sour, salty, and bitter. 1, 2
• Objective testing reveals much higher dysfunction rates (98.3% by UPSIT) than self-reported symptoms (35%), so patient assessment alone is unreliable. 1

Age-Related Physiological Changes (Most Common in Older Adults)

Sense of taste diminishes with increasing age due to physiological changes, disease, and medication use, leading older adults to compensate by increasing salt intake, which creates hypertension risk affecting over 50% of this population. 3, 4

• Age-related taste decline affects the ability to detect all five basic flavors, each serving specific nutritional functions. 4
• Sarcopenia affects swallowing muscles, reducing oral clearance and altering taste perception. 3
• Aging results in lower salivary flow rates, which combined with medication effects leads to xerostomia. 3

Medication-Induced Taste Disorders

Anticholinergic medications are major culprits, exacerbating taste dysfunction through multiple mechanisms affecting taste receptor function and reducing saliva production. 4

• Acetylcholinesterase inhibitors worsen taste perception by increasing saliva production and altering the oral environment. 4
• Many medications older adults consume contribute to decreased appetite, incoordination, and esophagitis. 3

Chronic Rhinosinusitis and Sinonasal Disorders

Chronic rhinosinusitis with nasal polyposis causes conduction loss from sinonasal passage obstruction, with CT-documented severity correlating with worse olfaction. 1

Neurological and Neurodegenerative Diseases

Alzheimer disease and Parkinson disease are strongly associated with olfactory dysfunction, which can serve as an early diagnostic marker. 1

• Parkinson's disease causes bradykinesia affecting oral and pharyngeal function, leading to saliva pooling and altered taste perception. 4
• Stroke affects taste pathways in 50% of patients with clinically significant dysphagia. 4
• Multiple sclerosis causes dysphagia in over one-third of patients, affecting taste through impaired oral clearance. 4
• Progressive neurologic diseases (dementia, amyotrophic lateral sclerosis) cause taste alterations through both direct neural pathway damage and secondary effects on swallowing. 4
• Depression is associated with olfactory dysfunction. 1

Head Trauma

Head trauma is one of the most common causes of smell disorders, particularly frontobasal trauma causing neural damage. 1

Oral and Dental Pathology

Chronic dental diseases, atrophic glossitis, and oral infections directly impair taste receptor function and are common in elderly populations with reduced manual cleaning ability and high dietary intakes of sugars and refined carbohydrates. 3, 4

• Poor dental hygiene and high intake of cariogenic foods (sugars, refined carbohydrates, sticky candies, crisps, biscuits) increase risk. 3, 4
• Peptic esophagitis from GERD affects 8-19% of adults and can cause taste disturbances. 4

Systemic Disease States

• Diabetes mellitus affects parasympathetic innervation and alters taste perception through autonomic dysfunction. 4
• Chronic kidney disease causes salivary disorders with altered composition affecting taste sensation. 4
• Cancer and gastrointestinal inflammatory disorders directly impact nutritional status and taste function. 4

Neoplastic and Inflammatory Lesions

• Tumors affecting the cribriform plate (squamous cell carcinomas, meningiomas, esthesioneuroblastomas) can impair olfaction. 1
• Inflammatory lesions such as sarcoidosis and granulomatosis with polyangiitis result in impaired olfaction. 1

Cranial Nerve Involvement

Bell's palsy (acute unilateral facial nerve paralysis) causes taste disturbance or loss from the anterior tongue, along with dryness of the mouth. 1

Common Clinical Pitfalls to Avoid

• Do not overlook COVID-19 as a potential cause, especially when taste/smell loss is the primary symptom without traditional nasal congestion or rhinorrhea. 1
• Do not rely on patient self-assessment of severity, as objective testing reveals much higher rates of dysfunction. 1
• Do not order unnecessary neuroimaging when there is a clear temporal relationship to viral infection. 1
• Do not allow patients to compensate for taste loss by increasing salt intake—this creates a dangerous cycle of hypertension risk in a population where cardiovascular disease is already a major modifiable risk factor. 4