Smell and taste disorders

Disease Description (Causes and Symptoms)

• Definition: Olfactory disorders (anosmia, hyposmia) are conditions in which a person cannot sense odors at all or can sense them only partially. Taste disorders refer to a decrease in or abnormality of the sense of taste (sweet, salty, bitter, and sour). It is common for the flavor of food to decrease due to abnormalities in the sense of smell.
• Main causes
  • Conductive causes: Odor molecules cannot reach the olfactory mucosa because of mechanical obstruction of the nasal cavity or paranasal sinuses — acute/chronic sinusitis, nasal polyps, nasal tumors, severe obesity, etc. Nasal congestion may occur alongside these conditions.
  • Sensorineural causes: Damage to the olfactory nervous system (olfactory nerve cells or central nervous system) — upper respiratory viral infections (damage to the olfactory nerves as a sequela), head trauma (axonal damage to the olfactory nerves), aging, smoking, exposure to toxic substances, metabolic or nutritional abnormalities (zinc or copper deficiency, vitamin deficiency), chronic renal failure, diabetes, hypothyroidism, etc. They may appear early in neurodegenerative diseases (Parkinson’s disease and Alzheimer’s disease). Iatrogenic causes, such as surgery and radiation, are also possible.
  • Main causes of taste disorders: Decreased saliva production (radiation therapy, Sjögren syndrome, anticholinergic drugs), medications (anticancer drugs, some rheumatologic medications), nutritional deficiencies (zinc, vitamins), infections, trauma, systemic diseases (such as Addison’s disease), aging, and oral lesions (such as lichen planus).
• Symptoms
  • Complete inability to smell (complete anosmia) or decreased ability to smell (hyposmia), odors being perceived differently (parosmia), or perceiving odors that are not present (phantosmia).
  • Decreased taste, abnormal taste (dysgeusia), decreased food flavor, loss of appetite, weight changes, depressed mood, and safety risks (inability to detect gas, smoke, or spoiled food).

Treatment Methods

• Principles of treatment by cause
  • Conductive causes (nasal and paranasal sinus diseases): If sinusitis or nasal polyps are the cause, treatment may include medication (antibiotics if necessary), nasal steroid sprays, short-term oral steroids, and, if necessary, endoscopic sinus surgery (such as polyp removal).
  • Sensorineural causes (especially post-infectious or traumatic): Medications that clearly restore recovery are limited. Short-term oral steroids or vitamin (such as vitamin A) and zinc supplementation may be attempted, but effectiveness varies greatly between individuals.
  • Taste disorders: Remove or correct the cause (medications, dry mouth, nutritional deficiencies, etc.) — changing medications, saliva substitutes (to relieve dry mouth), zinc (zinc gluconate) supplementation, and vitamin supplementation (niacin, vitamin A, etc.).
• Non-pharmacological treatment
  • Olfactory rehabilitation (olfactory training): Regular odor-stimulation training (regularly smelling four representative scents) has been reported to improve function and is recommended.
  • Lifestyle management: Enhance the taste and aroma of food (using spices and seasonings), chew food thoroughly, and strengthen safety measures (gas and smoke alarms, checking expiration dates).
• Procedures and surgery
  • If structural lesions of the nasal cavity or paranasal sinuses (polyps or tumors) are the cause, they can be corrected with endoscopic surgery.
  • If a central cause is suspected (such as a tumor), coordinated treatment with neurosurgery, otolaryngology, or neurology is provided based on CT/MRI findings.
• Precautions, complications, and prognosis
  • Possible safety risks (inability to detect gas, smoke, or spoiled food), nutritional imbalance, and depression.
  • Recovery varies depending on the cause and degree of damage: Conductive causes are more likely to improve after treatment, while sensorineural causes (especially those related to nerve ganglion damage or neurodegenerative diseases) may recover incompletely or remain long-term.
  • Some medications (such as steroids) carry a risk of side effects, so follow the doctor’s instructions.

Checklist Before an Outpatient Visit (Including Recommended Items and Sample Questions)

• Items to bring (recommended)
  • A list of currently taken medications (including prescription and nonprescription medications and supplements)
  • Notes on when the symptoms began (date, and whether the onset was sudden or gradual) and how the symptoms have progressed
  • Records of accompanying symptoms: nasal congestion, runny nose, nosebleeds, distorted sense of smell (parosmia or phantosmia), history of head trauma, history of colds or fever, changes in taste, weight changes, decreased saliva production, and oral lesions
  • Previous test results (recent CT/MRI, sinus examinations, blood tests, and previous smell or taste test results)
  • Occupational and lifestyle history (smoking, exposure to toxic substances, and whether radiation therapy or anticancer treatment was received recently)
• Materials to show the doctor during the outpatient visit
  • Medication list, symptom diary (when and what you are unable to smell), and photographs (if an oral or nasal lesion is suspected)
• Points to note before the examination
  • At the visit, provide an accurate list of medications whenever possible. Do not overlook a history of recent nasal surgery, head trauma, or other relevant conditions.

Examples of General Questions to Ask the Doctor

• "What tests are needed to determine the cause of these symptoms?"
• "What treatment options are available to me, and what effects (likelihood of recovery) can be expected?"
• "What are the side effects and precautions of the medications you prescribe?"
• "What should I be careful about in daily life (cooking, smoking, work, etc.)?"
• "If necessary, which specialists (neurology, oral medicine, psychiatry, etc.) will be consulted together?"

Examples of Condition-Specific Questions

• Related to olfactory disorders
  • "What tests are needed (such as endoscopy or CT) to determine whether my decreased sense of smell is caused by nasal congestion or nasal polyps?"
  • "How should I start olfactory rehabilitation (olfactory training), and how often should I do it for it to be effective?"
• Related to taste disorders
  • "Do I need testing for zinc deficiency or vitamin deficiencies (such as vitamin B or niacin)? If so, how likely is it that supplementation will restore my sense of taste?"

(Note: Diagnosis and treatment vary depending on the individual’s condition. Please have a specialist evaluate you before an accurate assessment and treatment plan are determined.)