Etiology of Loss of Taste (Hypogeusia)
Loss of taste is most commonly caused by viral upper respiratory infections (particularly COVID-19), medications, zinc deficiency, poor oral health, aging, and iatrogenic nerve damage from dental/oral procedures. 1, 2, 3
Viral Infections
- COVID-19 is now the predominant viral cause of taste loss, affecting 59-86% of infected patients 4
- Post-viral olfactory loss (PVOL) accounts for approximately 11% of community cases and 20-25% of specialist clinic presentations, with coronaviruses being a well-established cause 5
- The mechanism involves direct viral neurotropism to gustatory nerves, cytotoxicity to taste buds, and damage to olfactory epithelium 6
- Most taste loss in viral infections actually reflects loss of retronasal olfaction (flavor perception) rather than true taste dysfunction 5
- Traditional nasal symptoms (congestion, rhinorrhea) are often absent in COVID-19-related chemosensory dysfunction, unlike other viral respiratory infections 4
Medications and Systemic Factors
- Numerous medications can induce zinc deficiency, leading to taste disorders 7
- Systemic conditions including diabetes mellitus, chronic kidney disease, endocrine disorders, and autoimmune diseases cause dysgeusia 3
- Malnutrition and nutritional deficiencies, particularly zinc deficiency, are significant contributors 2, 7
- High alcohol consumption and cigarette smoking are environmental risk factors 2
Local and Iatrogenic Causes
- Iatrogenic nerve damage during dental procedures can cause taste loss through injury to the chorda tympani nerve (cranial nerve VII), lingual nerve, or glossopharyngeal nerve (cranial nerve IX) 8
- Specific dental risks include: third molar extractions, proximity of surgical site to chorda tympani nerve, lingual flap retraction, and direct needle trauma from local anesthetic injection 8
- Poor oral health and oral infections (viral, bacterial, fungal) contribute to taste dysfunction 2, 3
- Head trauma can damage the facial (VII), glossopharyngeal (IX), or vagus (X) nerves responsible for taste sensation 3, 8
Additional Contributing Factors
- Aging is a natural cause of progressive taste impairment 2
- Cancer treatment (radiation or chemotherapy) damages taste receptor cells 2, 3
- Chemical exposure and excessive use of disinfectants have been associated with dysgeusia 6
- Salivary gland disturbances affecting quality and quantity of saliva impair taste perception 6
- Pro-inflammatory cytokines and angiotensin II imbalance (particularly in COVID-19) contribute to taste dysfunction 6
Clinical Pearls
- Objective testing reveals higher rates of dysfunction than self-reported symptoms: 98.3% had olfactory dysfunction by UPSIT testing when only 35% reported taste/smell complaints 4
- Taste loss can present as the sole symptom without other respiratory manifestations, particularly in COVID-19 4
- The three cranial nerves mediating taste (VII, IX, X) have overlapping anatomic proximity with the trigeminal nerve (V), creating risk for combined sensory deficits during surgical procedures 8