Ageusia (from negative prefix ''a-'' and

Ancient Greek Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...

''γεῦσις'' geûsis 'taste') is the loss of

taste The gustatory system or sense of taste is the sensory system that is partially responsible for the perception of taste. Taste is the perception stimulated when a substance in the mouth biochemistry, reacts chemically with taste receptor cells l ...

functions of the

tongue The tongue is a Muscle, muscular organ (anatomy), organ in the mouth of a typical tetrapod. It manipulates food for chewing and swallowing as part of the digestive system, digestive process, and is the primary organ of taste. The tongue's upper s ...

, particularly the inability to detect sweetness, sourness, bitterness, saltiness, and

umami Umami ( from ), or savoriness, is one of the five basic tastes. It is characteristic of broths and cooked meats. People taste umami through taste receptors that typically respond to glutamates and nucleotides, which are widely present in me ...

(meaning 'savory taste'). It is sometimes confused with

anosmia Anosmia, also known as smell blindness, is the lack of ability to detect one or more smells. Anosmia may be temporary or permanent. It differs from hyposmia, which is a decreased sensitivity to some or all smells. Anosmia can be categorized int ...

– a loss of the

sense A sense is a biological system used by an organism for sensation, the process of gathering information about the surroundings through the detection of Stimulus (physiology), stimuli. Although, in some cultures, five human senses were traditio ...

of smell. True ageusia is relatively rare compared to

hypogeusia Hypogeusia can be defined as the reduced ability to taste things. Due to a lack of stratification, the prevalence of hypogeusia, as well as hyposmia, may not be accurately known. Additionally, reviews do not always make distinctions between ageusia ...

– a partial loss of taste – and

dysgeusia Dysgeusia, also known as parageusia, is a distortion of the sense of taste. Dysgeusia is also often associated with ageusia, which is the complete lack of taste, and hypogeusia, which is a decrease in taste sensitivity. An alteration in taste or ...

– a distortion or alteration of taste. Even though ageusia is considered relatively rare it can impact individuals of any age or demographic. There has been an increase in reported cases of ageusia, due to the COVID-19 pandemic making ageusia more commonly diagnosed than before.

Symptoms

The complete loss of taste.

Causes

Ageusia can arise from various factors: * Issues with the water-soluble molecules responsible for taste, causing oral dryness or damage to taste buds. *

Radiation therapy Radiation therapy or radiotherapy (RT, RTx, or XRT) is a therapy, treatment using ionizing radiation, generally provided as part of treatment of cancer, cancer therapy to either kill or control the growth of malignancy, malignant cell (biology), ...

treatments. * Facial nerve damage due to surgery. * Head traumas, traumas to middle ear or jaw. *

Sinusitis Sinusitis, also known as rhinosinusitis, is an inflammation of the mucous membranes that line the sinuses resulting in symptoms that may include production of thick nasal mucus, nasal congestion, facial congestion, facial pain, facial pressure ...

, strep throat, salivary gland infections, common cold,

influenza Influenza, commonly known as the flu, is an infectious disease caused by influenza viruses. Symptoms range from mild to severe and often include fever, runny nose, sore throat, muscle pain, headache, coughing, and fatigue. These sympto ...

, and

COVID-19 Coronavirus disease 2019 (COVID-19) is a contagious disease caused by the coronavirus SARS-CoV-2. In January 2020, the disease spread worldwide, resulting in the COVID-19 pandemic. The symptoms of COVID‑19 can vary but often include fever ...

. *

Bell's palsy Bell's palsy is a type of facial paralysis that results in a temporary inability to control the facial muscles on the affected side of the face. In most cases, the weakness is temporary and significantly improves over weeks. Symptoms can vary f ...

or dental procedures like a molar extraction and

tonsillectomy Tonsillectomy is a surgical procedure in which both palatine tonsils are fully removed from the back of the throat. The procedure is mainly performed for recurrent tonsillitis, throat infections and obstructive sleep apnea (OSA). For those wit ...

. *

Epilepsy Epilepsy is a group of Non-communicable disease, non-communicable Neurological disorder, neurological disorders characterized by a tendency for recurrent, unprovoked Seizure, seizures. A seizure is a sudden burst of abnormal electrical activit ...

, tumors, stroke, or

multiple sclerosis Multiple sclerosis (MS) is an autoimmune disease resulting in damage to myelinthe insulating covers of nerve cellsin the brain and spinal cord. As a demyelinating disease, MS disrupts the nervous system's ability to Action potential, transmit ...

. * Diseases that can affect the autonomic nervous system, like diabetes. * Some medications, including muscle relaxants, chemotherapy medication, anti-fungal, chemical compounds found in anti-depressants, anti-seizure medications, and blood pressure medications. *

Sialadenitis Sialadenitis (sialoadenitis) is inflammation of salivary glands, usually the major ones, the most common being the parotid gland, followed by submandibular and sublingual glands. It should not be confused with sialadenosis (sialosis) which is a ...

, gingivitis, oral infections, or glossodynia (burning mouth syndrome (BMS)). Ageusia resulting from a significant head injury is relatively uncommon, affecting only around 1% of individuals with this type of injury.

COVID-19

Ageusia can be an indication of a COVID-19 infection. Ageusia and anosmia are among the prominent symptoms commonly associated with COVID-19, with symptoms that could last up to 4 weeks. However, it is noteworthy that ageusia may manifest differently from anosmia, as anosmia primarily affects the olfactory system versus ageusia primarily affecting the gustatory receptors. As a result, emerging research indicates that the various

variants Variant may refer to: Arts and entertainment * ''Variant'' (magazine), a former British cultural magazine * Variant cover, an issue of comic books with varying cover art * ''Variant'' (novel), a novel by Robison Wells * " The Variant", 2021 epis ...

of COVID-19 might be associated with differences in the severity of ageusia experienced by patients, as well as the severity of other taste and smell disorders. Implying that certain strains of the virus may have differing impacts on the sensory functions of affected individuals. Studies investigating the prevalence of taste disorders stemming from the COVID-19 pandemic indicate that a wide range of individuals were impacted, with some experiencing these issues more severely than others: Patients with ageusia observed in 28.0% of patients,

in about 33.5%, and

in about 41.3% of patients. In April 2020, 88% of a series of over 400

disease patients in Europe were reported to report gustatory dysfunction (86% reported

olfactory The sense of smell, or olfaction, is the special sense through which smells (or odors) are perceived. The sense of smell has many functions, including detecting desirable foods, hazards, and pheromones, and plays a role in taste. In humans, it ...

dysfunction). Additionally, in South Korea, out of approximately 2,000 recorded cases of individuals with ageusia related infection from COVID-19, only 30% exhibited ageusia. The duration of ageusia recovery can vary significantly depending on cause of infection. In a COVID-19-related infection, the recovery timeline for ageusia can vary among individuals, influenced by factors such as variants or strains of the virus, individual immune responses, demographic characteristics, and other factors.

Proposed mechanisms of infection

Recent research has hinted at a connection between the distribution of taste cells and ACE2 receptors in ageusia. Higher amounts of the receptors suggests an easy route for a COVID-19 infection with a possible outcome of ageusia. Ageusia could also possibly occur due to changes in the abundance or lack of saliva that can eventually cause damage to the cells on the tongue's surface.

Saliva and taste perception

Saliva is essential in taste sensation and perception. Studies have indicated that saliva plays a critical role in detecting a COVID-19 infection, and ageusia can serve as an indication of an infection that is affecting the

salivary gland The salivary glands in many vertebrates including mammals are exocrine glands that produce saliva through a system of ducts. Humans have three paired major salivary glands ( parotid, submandibular, and sublingual), as well as hundreds of min ...

s. However, there is still insufficient research to fully clarify the full effects of ageusia, COVID-19, and their potential impacts on saliva and 'salivary flow rate.'

Zinc deficiency

In cases of zinc deficiency, a shortage of zinc-binding proteins that help with the growth and development of taste buds, could result in taste bud issues associated with ageusia, hypogeusia, and

hyposalivation Xerostomia, also known as dry mouth, is a subjective complaint of dryness in the mouth, which may be associated with a change in the composition of saliva, reduced salivary flow, or have no identifiable cause. This symptom is very common and is o ...

. Low levels of

cyclic adenosine monophosphate Cyclic adenosine monophosphate (cAMP, cyclic AMP, or 3',5'-cyclic adenosine monophosphate) is a second messenger, or cellular signal occurring within cells, that is important in many biological processes. cAMP is a derivative of adenosine tri ...

(cAMP) and

cyclic guanosine monophosphate Cyclic guanosine monophosphate (cGMP) is a cyclic nucleotide derived from guanosine triphosphate (GTP). cGMP acts as a second messenger much like cyclic AMP. Its most likely mechanism of action is activation of intracellular protein kinases in ...

(cGMP), which help with the growth of taste buds, in saliva have also been linked to ageusia.

Diagnosis

Ageusia is usually diagnosed by an

otolaryngologist Otorhinolaryngology ( , abbreviated ORL and also known as otolaryngology, otolaryngology–head and neck surgery (ORL–H&N or OHNS), or ear, nose, and throat (ENT)) is a surgical subspecialty within medicine that deals with the surgical an ...

, also known as an ear nose and throat doctor(ENT). These individuals can evaluate a patient's loss of taste among other things. To do this, a specialist will look into any other factors that could be causing ageusia, such as examining the head, nose, ears, and mouth. As well as imaging of the head and neck, to help further identify or eliminate the presence of tumors, focal lesions, or any type of injury that could possibly be affecting any taste-related networks. An otolaryngologist can also conduct a series of tests to assess the severity of ageusia, which includes identifying specific tastes that the patient can sense or recognize. An example of a test used by researchers and doctors is

electrogustometry Electrogustometry is the measurement of taste The gustatory system or sense of taste is the sensory system that is partially responsible for the perception of taste. Taste is the perception stimulated when a substance in the mouth biochemistry ...

. This test involves applying mild electric currents to specific tongue areas, to assess taste sensitivity in patients exhibiting ageusia and its symptoms. Another test that can be used to detect the severity of an individuals ageusia is an 'suprathreshold taste test,' also known as a edible strip taste test. The edible strip is placed on the individuals tongue and it contains various flavors for the patient to be able to detect, or not able to detect.

Treatment

Treatment for ageusia varies depending on its cause, whether it stems from certain illnesses, medications, traumatic injuries or other causes. If ageusia is triggered by a medication prescribed to a patient, discontinuing the medication under the guidance of a healthcare professional may alleviate the symptoms. Switching to an alternative medication can also help resolve the issue. In cases where ageusia is associated with an underlying illness or trauma, some medications can also help alleviate symptoms. Some of these medications include,

antihistamine Antihistamines are drugs which treat allergic rhinitis, common cold, influenza, and other allergies. Typically, people take antihistamines as an inexpensive, generic (not patented) drug that can be bought without a prescription and provides ...

s, decongestants, and antibiotics.

Complications

People experiencing ageusia can endure daily discomfort, which frequently diminishes their enjoyment of eating. This discomfort can cause many individuals affected by taste disorders with feelings of: * Isolation in individuals experiences * Feelings of depression * Social withdrawal * Unhealthy eating habits Such eating habits may involve either insufficient food intake or excessive consumption of sour or sweet foods. This dietary pattern could pose risks, particularly for individuals with diabetes.

Ageusia and Diabetes

Diabetes Diabetes mellitus, commonly known as diabetes, is a group of common endocrine diseases characterized by sustained high blood sugar levels. Diabetes is due to either the pancreas not producing enough of the hormone insulin, or the cells of th ...

has been shown to sometimes lead to ageusia, often starting with fluctuations in

glucose Glucose is a sugar with the Chemical formula#Molecular formula, molecular formula , which is often abbreviated as Glc. It is overall the most abundant monosaccharide, a subcategory of carbohydrates. It is mainly made by plants and most algae d ...

levels. When blood sugar levels fluctuate, it can disrupt the taste buds, making it difficult to detect flavors. But not everyone with diabetes will experience this. The severity of an individuals ageusia or other taste dysfunction can differ from person to person.

References

External links

* * * {{Taste Gustatory system Laryngology Symptoms and signs of mental disorders ru:Агевзия