Tasting is almost exclusively a function of our tongue. However, the sense of smell can also influence the perception of taste to a certain extent. Our tongues contain taste receptors that are responsible for identifying various chemicals in the food. Based on the unlimited variety of foods that humans consume through the course of their lives, one might assume that there are a huge number of taste receptors on the tongue. However, our tongues have a very limited repertoire of taste receptors.
Types of Tastes
In fact, only five types of taste receptors on the tongue are responsible for producing the variety of taste sensations we all experience. The five categories of taste receptors on the tongue are responsible for producing the following five primary taste sensations:
- Salty: The salty taste sensation is triggered by foods containing high concentrations of ionized salts (especially sodium ions).
- Sour: The sour taste sensation is triggered by acidic foods. These foods contain high concentrations of hydrogen ions.
- Sweet: The sweet sensations are triggered by a variety of organic compounds like sugars.
- Bitter: The bitter sensations are triggered by a wide variety of chemicals, especially long chain organic compounds containing nitrogen and alkaloids.
- Umami: Umami is a Japanese word for delicious. The umami taste sensation is triggered by foods containing L-glutamate. Examples include meat and certain aged foods.
The variety of taste sensations that we experience are produced by a combination of these five primary taste sensations.
Why are tastes offensive?
Sometimes, foods that are spoilt may taste bad. However, bad taste sensation in the mouth could also occur on its own, with no relationship to eating or drinking. It is common to get bad taste in the mouth that is not due to foul tasting food. The medical term used for this condition is cacogeusia.
The sensation of bad taste in the mouth that occurs in cacogeusia may or may not be psychogenic or imagined. The foul taste and smell sensations in cacogeusia usually have some underlying pathological basis. Sometimes, an alteration of the sensation of taste could make normal food or drink taste bad. This altered taste perception is medically termed as dysgeusia.
Read more on strange taste in the mouth.
Causes of Bad Taste in Mouth
A variety of conditions can lead to bad taste sensation in the mouth, which may or may not be accompanied by bad sensations of smell (technically known as cacosmia). The most common causes of bad taste sensations in the mouth are pathologies within the mouth itself. In addition, gastrointestinal disorders and problems within the airways and the lungs could also lead to cacogeusia.
In most cases of cacogeusia that are due to pathological causes, bad breath (technically known as halitosis) is also frequently present. Halitosis is absent in cases of cacogeusia resulting from medications and psychogenic causes. In cases of cacogeusia where offensive odors are perceived even when they are absent in the environment, infections of the sinuses and the respiratory tract should be investigated.
Problems with teeth and gums
One of the most common causes of bad taste in the mouth is dental cavity. The bad taste sensation associated with tooth cavities are due to the decomposition of the food particles lodged in these cavities. Halitosis (bad breath) is also associated with this condition. Apart from the teeth, diseases of the gums can also lead to bad taste sensations in the mouth, frequently accompanied by halitosis. Examples of such diseases include periodontitis and gingivitis.
Problems in the mouth
Besides pathological states of teeth and gums, other conditions in the oral cavity could also lead to bad taste in the mouth. For example, mouth sores (also called apthous ulcers), cancers in the oral cavity and inflammation of the mouth and lips (also known as stomatitis) can also lead to bad taste sensations. Infections in the mouth are frequently responsible for cacogeusia.
Diseases of the throat, such as pharyngitis and tonsillitis, may also cause bad taste sensations in the mouth. A dry mouth (technically referred to as xerostomia) is also associated with cacogeusia. However, cacogeusia seen in dry mouth is usually secondary to infections of the mouth and teeth that result from reduced production of saliva.
Various types of gastrointestinal conditions could result in a bad taste in the mouth. For example, cacogeusia could be caused by conditions such as pyloric stenosis and gastroparesis. These conditions are characterized by impaired gastrointestinal motility resulting in decomposition of food. Gastritis, due to infectious causes, can also cause bad taste in the mouth.
Cacogeusia may also be a result of retrograde flow of partially digested or decomposed food and stomach acid into the throat and mouth. This condition is medically known as gasroesophageal reflux disease (commonly abbreviated as GERD). The bad taste in the mouth due to gastroesophageal reflux disease is usually worse in the mornings and is accompanied by persistent sore throat and foul morning breath.
Problems in respiratory system
Apart from pathological conditions of the gastrointestinal tract, bad taste in the mouth could also result from respiratory problems. Infectious conditions affecting both airways and lungs could result in cacogeusia. Halitosis is also frequently associated with these infectious conditions of the respiratory tract. Examples of respiratory tract conditions that may cause bad taste in the mouth include tuberculosis, lung abscess, gangrene, and bronchiectasis.
Certain medications have been implicated as potential causes of bad taste in the mouth. Examples of suspected medicines include antibiotics, proton pump inhibitors (abbreviated as PPIs), and oral contraceptives. However, evidence against these medications are inconclusive. There may be other factors at play.
Bad breath is a frequent complaint in diabetes. This is usually caused by ketoacidosis that is a characteristic feature of the pathology of this disease. In some cases, bad taste in the mouth is also reported by diabetic patients. This is usually seen in case of uncontrolled diabetes, and is attributed to dental caries and stomatitis that occur in this condition. Halitosis is also present alongside cacogeusia in this condition.
Bad taste in the mouth may also have psychogenic causes. However, the above mentioned pathological causes must be ruled out before attributing cacogeusia to psychogenic causes.