What are the causes and treatments for loss of taste?

Loss of Taste: Causes and Treatment

Primary Causes

The most common cause of taste loss is actually olfactory (smell) dysfunction rather than true gustatory impairment, accounting for approximately 95% of perceived taste disorders. 1

Viral Infections (Most Common in Current Context)

• COVID-19 is now a leading cause, affecting 59-86% of infected patients 2, with loss of taste/smell occurring as the initial or isolated symptom in 11.9-22% of cases 2
• Traditional upper respiratory viral infections remain common causes, though COVID-19 distinctively causes chemosensory loss without typical nasal congestion or rhinorrhea 2
• Post-viral olfactory loss accounts for 20-25% of specialist clinic presentations 3

Sinonasal Disease

• Chronic rhinosinusitis (with or without polyps) is a major cause 1
• Allergic rhinitis frequently impairs smell and taste 1
• Nasal obstruction or inflammation should be identified on examination 4

Other Important Causes

• Medications are a frequent culprit 1
• Head trauma can damage olfactory pathways 1
• Neurodegenerative diseases including Parkinson disease 1
• Aging-related physiological changes 5
• Poor oral health and dental disease 5
• Smoking, high alcohol consumption, and malnutrition 6

Diagnostic Workup

Initial Assessment

• Obtain detailed history focusing on onset timing, duration, and temporal relationship to viral infections (especially COVID-19) 4
• Document associated symptoms including nasal obstruction, rhinorrhea, or flu-like illness 3
• Perform thorough nasal examination for signs of obstruction or inflammation 4
• Examine the mouth, oropharynx, and perform neurologic examination focusing on cranial nerves I, VII, IX, and X 1

Objective Testing

• Standardized psychophysical testing using validated instruments (UPSIT or Sniffin'Sticks) is mandatory, as patients cannot accurately assess their own impairment severity 3
• These tests have high test-retest reliability and take 4-25 minutes to administer 3
• In COVID-19 context, objective testing reveals dysfunction in 98.3% of patients even when only 35% report symptoms 2

COVID-19 Specific Testing

• Perform COVID-19 testing in all patients with sudden-onset taste/smell loss, especially during pandemic periods 3
• Loss of taste/smell may be the sole presenting symptom requiring testing 3

Advanced Imaging

• Order CT and MRI of skull base and brain only when psychophysical testing severity does not correlate with endoscopic findings, raising suspicion for occult sinonasal or skull base tumor 3
• Avoid unnecessary neuroimaging when there is clear temporal relationship to viral infection 4

Treatment Approach

Primary Treatment Strategy

Olfactory training is the primary treatment for persistent taste/smell loss and should be started immediately, continuing for at least 3-6 months 4

Treating Underlying Causes

• Treat sinonasal inflammatory disease with appropriate medical or surgical management 3
• Address poor oral health and dental disease, particularly in older adults 5
• Review and modify medications if possible 1

Dietary Management

• Refer patients to a registered dietitian for dietary counseling focusing on additional seasoning of food, avoiding unpleasant foods, and expanding dietary options 4
• Use flavor enhancers to promote food intake in individual cases 4
• For older adults at risk, use herbs and spices instead of salt to avoid hypertension risk 5

Pharmacologic Considerations

• Based on research evidence, phosphodiesterase inhibitors, insulin, and corticosteroids show promise for COVID-19-related smell and taste loss 7
• However, guideline-level recommendations prioritize olfactory training over pharmacologic interventions 4

Recovery Timeline and Prognosis

• For COVID-19 patients: 73% improve within 7-14 days, though 20% have symptoms persisting beyond 14 days 2
• Recovery occurs in 44-73% of COVID-19 patients within the first month 3
• Up to one-half of patients with olfactory dysfunction from all causes improve over time 1
• Improvement is inversely correlated with severity and duration of loss, age, smoking, and male sex 1

Follow-Up Protocol

Re-evaluate patients at 1 month, 3 months, and 6 months after initiating treatment 4

• Repeat psychophysical testing at follow-up visits to objectively document changes 3
• Refer to an otolaryngologist or specialized smell and taste clinic if no improvement after 3-6 months 4

Critical Safety Considerations

Address potential safety concerns related to inability to detect spoiled food or gas leaks 4

• This puts patients at higher risk for toxic exposures including gas leaks, smoke, and rotting food 8
• Provide counseling on compensatory safety strategies

Common Pitfalls to Avoid

• Do not overlook COVID-19 as a potential cause, especially when taste/smell loss is the primary symptom 4
• Do not rely on patient self-assessment of impairment severity—always use objective testing 3
• Do not assume taste loss is purely gustatory—remember that 95% is actually olfactory dysfunction 1
• Do not order neuroimaging reflexively when viral etiology is clear 4