Unable to taste food - well, you’re not alone. Ageusia is a condition that has been on the rise since 2019, a surge attributed mainly to post-viral syndromes, which have stripped 1 or 2 out of 1000 people of their ability to taste food properly.¹ This emphasises exploring diagnostic algorithms for ageusia- whether due to ENT-related conditions, or neurological complications, accurate diagnosis is crucial to restoring taste.

What is ageusia

Ageusia is a condition that exists as a symptom of various underlying pathological conditions. It’s often characterised as the complete loss of taste, which in turn takes the joy out of eating. Eating is a crucial component of our social, personal, and physical well-being; therefore, a loss of taste can lead to mood changes, malnutrition, and the inability to distinguish spoiled foods. 

Increased awareness of ageusia in recent times has led to systematic diagnostic approaches for evaluating patients suffering from Ageusia. This approach follows a detailed review of a patient's clinical history, followed by an ENT examination. If initial findings are inconclusive, then patients would be referred for taste tests, laboratory testing, and imaging procedures to rule out nutritional or neurological abnormalities.²

Step 1: clinical history and symptom review

The two main etiological factors causing olfactory dysfunction are:

• Conductive losses: issues concerning obstruction in the nasal pathways 
• Sensory/neural losses: damage or dysfunction of olfactory nerves or other related neural centres

The most essential step in evaluating a patient suffering from a smell disorder is to review their clinical history and define their symptoms. This involves description of the patient's ability to taste before the loss, in addition to the onset, duration and other associated symptoms. The examiner should question the patient about events that occurred before the initial loss, such as:

• Head trauma
• Nasal Surgery
• Exposure to toxins or fumes
• Upper respiratory infections (URIs)

All of which are established risk factors. Clinicians also inquire about congestion, sinus pain, nasal blockage, or epistaxis (nosebleeds), which may raise concerns for sinonasal tumours that require further medical imaging. 

Moreover, knowledge of symptoms such as congestion, sinus pain, nasal blockage, or fluctuating taste symptoms could suggest potential sinus infections that would require evaluation by an ENT specialist. 

Further relevant history about a patient’s medication or lifestyle provides insights into potential interferences with taste. For example, antimicrobials (i.e., penicillin) can temporarily disrupt olfactory function, whereas lifestyle factors such as smoking gradually dull senses over time. Attention must also be paid to signs of early dementia, Parkinson’s disease, depression, or schizophrenia, as symptoms of distorted taste are often a sign of underlying neurological or psychiatric conditions. By narrowing down the context and symptom profile of a patient, clinicians can decide whether to move forward with an ENT assessment or refer for neurological imaging.³

Step 2: ENT assessment

After a detailed evaluation of a patient’s history, it is crucial to perform a comprehensive assessment of the ears, nose, and throat (ENT). The most effective way to examine nasal obstruction would be a nasal endoscopy. This procedure involves using a rigid tube with a camera and light attached to look at the nasal and sinus passages. During a nasal endoscopy, clinicians look for:

• Nasal polyps or tumours
• Swelling or inflammation of the nasal and sinus linings
• Scar tissue or postoperative changes 
• Crusting 
• Narrowing or blocking of the airways

As all of these are abnormalities that interfere with the ability to smell, and by extension, affect the ability to taste.⁴

Following the physical examination, if a clinician notices anomalies such as unilateral nasal blockages, anatomical deformities, asymmetrical findings, polyps or tumours, then a CT scan of the sinuses is required. If the scan indicates the presence of an intranasal mass, then further evaluation with an MRI of the sinuses and skull base can detect intracranial extension (spread of malignant tumours).

Olfactory testing

In addition to physical examinations, olfactory testing is a key component of an ENT assessment. A standardised olfactory test has two main factors: taste and smell dysfunction. To assess taste function, clinicians may use tools such as: 

• Electrogustometry: applying a small electrical current to different taste buds for the detection of sour or metallic sensations
• Chemogustometry: using specific taste solutions to assess taste sensitivity 
• Taste strips: asking patients to identify the taste of filter paper saturated in certain tastants. Placing the paper on different parts of the tongue assesses regional taste function.³

If patients can pass the various taste tests, then clinicians may assess olfactory senses through smell identification tests, such as:

• University of Pennsylvania Identification Test (UPSIT): a test consisting of four ‘scratch and sniff’ booklets containing different odorants. Patients are then required to choose an answer to each odorant.
• Sniffin‘ sticks: a test primarily used in Europe that uses odorised felt-tipped pens that assess threshold, discrimination, and identification of olfactory senses

Step 3: rule out systemic and metabolic causes

When an ENT assessment fails to provide an apparent cause of olfactory dysfunction, clinicians will then move on to the next phase of the diagnostic algorithm: investigating systemic, metabolic, or nutritional factors.

Nutritional deficiencies 

Testing for nutritional deficiencies requires running blood tests to identify a deficit in the following vitamins and minerals:

• Vitamin B12
• Zinc

A lack of such nutrients may cause impairment of taste bud function and disrupt the perception of flavours.²

Systemic causes

A detailed review of a patient’s current and past medications may also uncover the reason behind olfactory losses. Certain medications, such as:

• ACE inhibitors 
• Chemotherapy agents
• Antibiotics (penicillins)
• Antidepressants 

These are their well-known systemic causes to induce temporary or chronic taste disturbances 

Moreover, additional screening for conditions including:

• Oral conditions: dry mouth syndrome and tongue inflammation 
• Autoimmune diseases: Sjrögen’s syndrome
• Respiratory infections: COVID-19, influenza, common cold

These impact our sense of smell or impair our salivary glands, preventing us from sensing taste.

Metabolic conditions such as diabetes can also reduce saliva flow, leading to dry mouth that can disrupt taste. Moreover, diabetes can lead to peripheral neuropathy, thereby affecting nerves responsible for taste perception. 

Congenital conditions such as Down syndrome can also contribute to taste and smell dysfunction due to a range of factors, including craniofacial differences, ENT abnormalities, and neurological underdevelopment.

When symptoms persist despite correcting for various systemic causes, it raises the possibility of neurological involvement. This leads to the next step of the diagnostic algorithm: neurological examination and imaging. 

Step 4: neurological evaluation

Suppose a patient’s ENT findings and systemic screenings prove to be inconclusive in finding the root cause of their ageusia. In that case, it is pertinent for a clinician to start evaluating the central nervous system (CNS) or cranial nerves involved in taste and smell.

Cranial nerve examination 

Taste sensations are mediated by the cranial nerves I, VII, IX, and X.⁵ When examining cranial nerves, clinicians typically assess:

• Facial asymmetry: asking patients to perform movements on only one side of the face, or examining any visual asymmetries. Asymmetry may suggest potential nerve damage.
• Taste sensation: applying sweet, sour, salty, and bitter tastants and quizzing the patient on the taste sensation and where on the tongue the tastant was placed 
• Testing for motor movements, such as a gag reflex

Apparent signs of facial asymmetry, lack of taste sensations, or impaired movements involving the face, palate, or gag reflex may indicate damage to cranial nerves responsible for taste and oral motor control.⁶

Brain imaging

If the diagnostic algorithm suggests that the main culprit in ageusia involves our central nervous system, or a patient presents unusual patterns that deviate from a standard diagnosis, then imaging becomes essential. Brain MRIs are typically preferred over CT scans as they offer better resolution of neural structures. When conducting an MRI scan, clinicians look out for:

• Tumours: present in areas affecting olfactory pathways 
• Structural loss/damage: caused by lesions from strokes or head trauma

Imaging is crucial in ruling out or confirming the presence of damage to the key vital structures in the CNS: the brain stem, thalamus, or pons.¹

Psychiatric or neurodegenerative disorders

Smell and taste changes can often be early indicators of neurodegenerative diseases such as Parkinson’s or Alzheimer’s. In many of these cases, loss of olfactory function can be attributed to ageing.

In sporadic cases, a patient may have distorted taste sensations as a result of their psychiatric disorders. For example, schizophrenic patients may present with olfactory hallucinations, with psychosomatic anosmia (loss of smell due to psychological factors) being a symptom of a hysteric episode.³

Limitations of current diagnostic pathways

Around 30–40% of ageusia cases remain without a clear cause, highlighting the diagnostic challenges clinicians face. Psychological effects, such as low mood or depression, are common and require sensitive communication. The subjective nature of symptom reporting further complicates diagnosis, as patients often struggle to distinguish between true taste loss and olfactory dysfunction, which affects flavour perception. Without access to objective testing, this can lead to misdiagnosis. A thorough, multidisciplinary approach is essential to identify the cause and provide appropriate support accurately.

Prognosis, outpatient management, and follow-up

While some cases of ageusia are treatable, some patients may experience permanent loss of taste. This can lead to psychological issues; therefore, developing a robust treatment plan may provide support to patients. 

Some taste disorders can be solved instantly by stopping certain medications, whereas other cases require time. This may involve taking certain supplements to replenish nutrients or engaging in therapies to fix nerve damage.

Lastly, all patients must follow a well-balanced diet, with more frequent, smaller meals and attentive care to their oral hygiene. A personalised care plan and detailed education for all patients is therefore crucial in improving outcomes and overall quality of life.¹

Summary

Ageusia is a complex condition with a broad differential diagnosis, which makes it essential to have a communicative interprofessional team. A structured algorithm beginning with clinical history, followed by ENT and neurological evaluations, helps streamline the diagnostic process and improve patient outcomes. 

FAQs

Q1: Is ageusia always caused by COVID-19?

No. While COVID-19 has been linked to temporary loss of taste, many other causes exist, including ENT issues, neurological conditions, medications, and nutritional deficiencies.

Q2: What’s the difference between ageusia and dysgeusia?

Ageusia refers to the complete loss of taste, while dysgeusia describes distorted or altered taste sensations.

Q3: What kind of doctor should I see first for loss of taste?

An ENT specialist is usually the first point of contact, followed by a neurologist if initial exams don’t reveal a clear cause.

Q4: Can ageusia be permanent?

In some cases, especially when linked to nerve damage or chronic conditions, ageusia may persist. However, many causes are treatable or reversible.

Q5: Can I prevent ageusia?

Ageusia often results from a separate condition, so it’s not always preventable. However, you can reduce your risk by keeping your mouth moist, taking B12 and zinc supplements, and making oral hygiene a priority.