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 Hyposmia, or microsmia, is a reduced ability to smell and to detect odors. A related condition is anosmia, in which no odors can be detected. Some of the causes of olfaction problems are allergies, nasal polyps, viral infections and head trauma. ...

, may not be accurately known. Additionally, reviews do not always make distinctions between

ageusia Ageusia (from negative prefix ''a-'' and Ancient Greek ''γεῦσις'' geûsis 'taste') is the loss of taste functions of the tongue, particularly the inability to detect sweetness, sourness, bitterness, saltiness, and umami (meaning 'savory t ...

and hypogeusia, often classifying them as the same in certain circumstances and studies. The severity of the loss of taste from hypogeusia is not clearly outlined in current research due to these reasons.

Causes

Covid-19

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 ...

causes symptoms that affect the central nervous system (CNS), peripheral nervous system (PNS), and

skeletal muscle Skeletal muscle (commonly referred to as muscle) is one of the three types of vertebrate muscle tissue, the others being cardiac muscle and smooth muscle. They are part of the somatic nervous system, voluntary muscular system and typically are a ...

. Hypogeusia falls under a neurological disease and a PNS symptom, while also being the highest occurring PNS symptom, closely followed by

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 ...

. Due to hypogeusia being a significant symptom of COVID-19, it is often accompanied by

, even when many other COVID-19 symptoms are absent. Both can be considered early indications of a COVID-19 infection. Further, hypogeusia is often developed following early symptoms of hyposmia, usually developed from olfactory epithelium damage from upper respiratory infections.

Oral cancer

Hypogeusia tied to

oral cancer Oral cancer, also known as oral cavity cancer, tongue cancer or mouth cancer, is a cancer of the lining of the lips, mouth, or upper throat. In the mouth, it most commonly starts as a painless red or white patch, that thickens, gets ulcerated ...

and

tumors A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...

can affect sweet, sour, salty, and bitter tastes, but bitter taste hypogeusia occurs significantly more often compared to the rest of the tastes. Inhibition of

gustatory papillae 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 reacts chemically with taste receptor cells located on tas ...

found in the base, often due to oropharyngeal tumors, is thought of to be the cause of this. Oral cancer treatments, such as

chemotherapy Chemotherapy (often abbreviated chemo, sometimes CTX and CTx) is the type of cancer treatment that uses one or more anti-cancer drugs (list of chemotherapeutic agents, chemotherapeutic agents or alkylating agents) in a standard chemotherapy re ...

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), ...

, and surgical treatments, are further causes of taste and smell loss with up to 70% of oral cancer patients noting

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 ...

. Specifically, chemotherapies and radiation treatments may impair or damage various taste related cells, and certain surgeries may even remove minor to major parts of the tongue depending on the severity of the tumor.

Other

Nutritional

zinc deficiency Zinc deficiency is defined either as insufficient body levels of zinc to meet the needs of the body, or as a zinc blood level below the normal range. However, since a decrease in blood concentration is only detectable after long-term or severe ...

may cause various problems, hypogeusia being one of them. Chronic Rhinosinusitis (CRS) may cause olfactory dysfunction as well as gustatory problems, with either or both leading to the noticeable presence of hypogeusia in CRS patients. The connection between hypogeusia and

Parkinson's Disease Parkinson's disease (PD), or simply Parkinson's, is a neurodegenerative disease primarily of the central nervous system, affecting both motor system, motor and non-motor systems. Symptoms typically develop gradually and non-motor issues become ...

is less well described. PD patients have an increased dysregulation in their taste receptors, as well as their olfactory receptors. The receptors affected in PD patients were those associated with the perception of bitterness in most cases.

Treatment

Covid-19

Hypogeusia tied to COVID-19 can serve as an indicator of COVID-19, which can allow appropriate treatments to be administered earlier to patients.

Oral cancer

When treating oral cancer and related tumors, there is no clear treatment for hypogeusia. Precautions need to be studied and taken to prevent hypogeusia and related symptoms from forming. However, if the treatments have led to the formation of hypogeusia, than patient specific nutrition plans may be used to treat the loss of taste.

Other

While zinc supplementation may treat certain taste dysfunctions, there is a lack of evidence for treatment regarding hypogeusia and dysgeusia not caused by low zinc concentrations in the body. While the mechanisms surrounding hypogeusia from PD are hypothesized, specific treatments are not researched enough. Similarly, while treatment of olfactory related issues is known in CRS research, the treatment of gustatory problems, including hypogeusia, are unknown.

References

{{Reflist Gustatory system Symptoms and signs of mental disorders