What underlying medical conditions can cause loss of taste?

Underlying Medical Conditions Causing Loss of Taste

Loss of taste is most commonly caused by viral upper respiratory infections (including COVID-19), sinonasal inflammatory disease, head trauma, neurodegenerative disorders, and medications—with the majority of cases actually representing loss of retronasal olfaction (flavor perception) rather than true taste dysfunction. 1, 2, 3

Primary Categories of Causative Conditions

Viral and Infectious Causes

• COVID-19 infection is now recognized as a leading cause, affecting 59-86% of infected patients, with loss of taste/smell often presenting as the initial or sole symptom in 11.9-22% of cases 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 4, 2
• Upper respiratory infections including influenza commonly damage the olfactory neuroepithelium, which secondarily affects taste perception 1, 3
• Viral infections can cause epithelial disorders involving sensory cells that rarely respond to treatment 5

Sinonasal and Structural Disorders

• Chronic rhinosinusitis with nasal polyposis causes conduction loss from sinonasal passage obstruction, with CT-documented severity correlating with worse olfaction 1
• Nasal polyps, deviated nasal septum, and chronic sinusitis reduce airflow through the olfactory cleft at the roof of the nasal cavity 5
• These structural problems can be corrected by modern endoscopic surgery 5

Neurological and Neurodegenerative Conditions

• Alzheimer disease and Parkinson disease are strongly associated with olfactory dysfunction, which can serve as an early diagnostic marker 1, 6
• Mild cognitive impairment and dementia commonly present with smell and taste disorders 6
• Temporal lobe dysfunction can cause hallucinations or delusions in the sense of smell 1
• Multiple sclerosis and seizure disorders frequently involve chemosensory disturbances 6

Traumatic Causes

• Head trauma is one of the most common causes of smell disorders, particularly frontobasal trauma causing neural damage 1, 5, 7
• Dental procedures can cause nerve damage to the chorda tympani or lingual nerve during posterior mandibular surgery, resulting in irreversible gustatory deficits 8
• Trauma, aging, and inflammatory sinonasal disorders most commonly affect the sense of smell 1

Neoplastic and Inflammatory Lesions

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

Congenital and Developmental Conditions

• Kallmann syndrome and cephaloceles are congenital conditions that can result in impaired olfaction 1

Medication and Toxic Exposures

• Drugs are common offenders in taste dysfunction, though specific agents are not detailed in the guidelines 7
• Toxic destruction of sensory epithelium from solvents or gases can cause epithelial disorders 5
• Local anesthetic injection during dental procedures can cause direct needle trauma or neurotoxic effects 8

Metabolic and Systemic Disorders

• Endocrine, metabolic, and autoimmune disorders can affect taste perception 8
• Salivary gland disorders alter the fluids bathing chemoreceptors 8, 7
• Malnutrition disturbs the cycle of regeneration of chemoreceptors 7

Psychiatric and Mood Disorders

• Depression is associated with olfactory dysfunction 1

Critical Clinical Distinction

Most taste loss in viral infections actually reflects loss of retronasal olfaction (flavor perception) rather than true taste dysfunction, as true taste only differentiates four qualities: sweet, sour, salty, and bitter 2, 5. The typical flavor of food or drink is detected by olfaction, not taste 5.

Common Pitfalls

• Overlooking COVID-19 as a potential cause, especially when taste/smell loss is the primary symptom without traditional nasal congestion or rhinorrhea 9, 2
• Relying on patient self-assessment of severity, as objective testing reveals much higher rates of dysfunction (98.3% by UPSIT testing versus 35% self-reported) 2
• Ordering unnecessary neuroimaging when there is a clear temporal relationship to viral infection 9

Cranial Nerve Involvement

The sensation of taste is mediated by three cranial nerves: facial nerve (CN VII), glossopharyngeal nerve (CN IX), and vagus nerve (CN X), with the trigeminal nerve (CN V) providing overlapping general sensory innervation 8. Bell's palsy (acute unilateral facial nerve paralysis) can cause taste disturbance or loss from the anterior tongue, along with dryness of the mouth 1.