Aguesia, or the complete loss of taste, can be a confusing symptom with many possible causes. Whether it occurs suddenly or develops over time, understanding the underlying neurological mechanisms of Ageusia is essential to the management and treatment of the condition. 

This article explains how taste loss can result from peripheral issues that affect the taste signal before it enters the brain, or central issues that occur within the brain. 

Introduction

Ageusia is defined as the complete loss of taste. This means that people with this condition cannot taste salty, sweet, sour, bitter, and umami food flavours. Although it may seem relatively harmless, it can have a profound effect on appetite, nutrition, and overall well-being. 

All of the taste senses are very complex operations that require a lot of different signal inputs and outputs to and from the tongue and the brain (via neurons) to work properly. The problem arises when something malfunctions or is damaged somewhere along this pathway of signalling, leading to major consequences in the whole system. These problems can be peripheral (affecting the nerves before they reach the brain) or central (affecting the nerves inside the brain). 

This article provides a neurological perspective on Ageusia and what the different causes mean in terms of treatment and management of the disorder.  

How we taste: A simple breakdown

All of our senses have evolved for the purpose of survival, as a way to gather information about the world around us. Taste is important in making sure we don’t eat spoiled foods and in allowing us to process additional information regarding the food we ingest, such as the identity or concentration of the substance we ingest. 

Key parts of the taste system

Taste buds on the tongue and in the mouth

Different types of taste buds pick up different chemical signals from your food. For example, the chemical signal received from sour foods is acidic and releases hydrogen ions, which are detected by specific taste buds. 

Specific nerves or neurons that carry taste signals to the brain

Once a signal is detected by a taste bud, the signal is sent to neurons, which then send this signal to the brain. The main nerves that play a role in taste include the facial nerve, the glossopharyngeal nerve, and the vagus nerve.

Brain areas that process the information received 

The information ends up in a region of the brain called the gustatory cortex, where it is processed. 

Specific nerves that send the processed information from the brain to specific muscles in response

When the brain processes the taste information, it decides on whether to promote functions like salivation and swallowing or reject the food by gagging or vomiting. 

Peripheral causes of ageusia

Peripheral causes of Ageusia are causes related to damage or dysfunction of taste pathways before they reach the brain. This can occur anywhere from the taste buds – affecting how the signal is created in the first place – to the neurons that carry the taste signal to the brain. 

Examples of peripheral causes of Ageusia include:

• Nerve damage, which can be a result of:
  • Dental work¹ 
  • Burns
  • Surgery and local anaesthetic 
  • Bell’s palsy (a condition affecting the facial nerve)²
• Infections or inflammation in or around the mouth 
• Certain medications, for example, specific:
  • Antibiotics
  • Blood pressure medications 
  • Pain medications
  • Asthma drugs
  • Diabetes drugs
  • Antacids
  • Drugs for mental health, like ADHD medicines or antidepressants
  • Statin drugs
• Cancer treatments 
• Vitamin or mineral deficiencies 
• COVID-19 or other viruses

Central causes of ageusia

Central causes of Ageusia are related to damage or dysfunction of taste pathways in specific areas of the brain or spinal cord. This can occur in different ways, for example, due to:

• Parkinson’s disease³ 
• Stroke⁴
• Traumatic brain injury⁵
• Brain tumours or operations associated with their removal⁶ 

The central causes of Ageusia are usually more complex than the peripheral causes and can therefore be harder to treat or resolve. 

Diagnosis: What doctors look for

When seeking medical treatment for Ageusia, the medical professional may:

• Ask questions about medical history, including:
  • Recent illness
  • Medications
  • Injuries
  • Surgeries 
• Perform a physical examination of the mouth 
• Perform various tests to assess the severity of dysfunction to determine whether it is a complete taste loss or just a change in taste 
• Perform a psychological assessment, as certain medical conditions, like depression, can impact taste 
• Order medical imaging of the brain and spinal cord 

Ageusia may be a sign of a serious underlying condition; hence, early diagnosis and further testing to determine the cause of Ageusia are essential. 

Treatment options

There is no one-size-fits-all solution for restoring taste loss. The general guide to the treatment of Ageusia is to treat the underlying condition if possible. This may look like:

• Treating the cause of infections
• Adjusting medications
• Managing nerve injuries
• Taking supplements for vitamin or mineral deficiencies

In some cases, taste can return spontaneously without any treatment or adjustment. 

Living with ageusia

As there is no current cure for Ageusia, it is important for patients experiencing this condition to learn how to cope with it. Ageusia can have a profound effect on appetite (which can lead to excessive weight loss/gain or development of disordered eating in some individuals), mood, and general quality of life. 

Coping strategies include:

• The use of condiments, sauces, and fats to enhance flavour
• Eating smaller and more frequent meals
• Oral care
• A focus on texture, temperature, and smell when eating

Summary

The sense of taste is a complex biological function which involves the working together of many different receptors (taste buds) and neurons. Ageusia, the complete loss of taste, can be caused by problems in the nerves outside the brain (such as nerve damage or medication side effects) or by conditions that affect the brain itself (due to conditions like stroke, Parkinson’s disease or traumatic brain injury). 

Diagnosis of Ageusia involves a combination of evaluating medical history, physical and psychological evaluations, and imaging techniques. Although treatment depends on the cause and no cure exists for Ageusia, symptom management, dietary strategies, and lifestyle adaptations can help improve the quality of life of those affected.