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Dental and Oral Health Center

Bitter Taste Back 1/3 of Tongue/Soft Palate

09/02/2009

Question:

Two days ago, almost spontaneously, I started to experience a bitter taste on the back 1/3 of my tongue and soft palate. It reminded me of the taste of an uncoated aspirin or envelope glue(neither of which I had injested). It has not resolved. Some foods have an altered taste now, like bananas, cherries, zuchini bread. I seem to notice when I am eating something sweet, often the bitterness is exacerbated. I`m nervous and frustrated. Is this serious? How can it be treated?

Answer:

Alteration in taste is a very complex problem and could be the result of many different things.

The etiology of some taste disturbances can be linked to infections (viral, bacterial, and fungal). These occurrences in most cases are transient and resolve after the infection clears. Head trauma (concussive injury and closed head injury) have been associated with taste disorders and in this case nerve damage to the nerves that supply the taste buds. (In many cases, smell is also affected.)

It is interesting that you complain of "bitter" taste as this specific taste sensation plays a dual role in humans; aversion or a warning signal (poisons/toxins) and that of an attractant (in the case of mildly bitter taste in hops/beer, wine, tonic water, and some cheeses). The bitterness is the result of a large number of varied compounds such as amino acids and peptides, polyphenols like tannins, and anthocyanins (grape skins, tea), glucosinolates from cruciferous vegetables like broccoli, kale, collards. Some persons are more sensitive than others in tasting or discerning bitter sensation.  This is exemplified by the wide variation of individuals that can taste the chemical substance "PROP" or 6-n-propylthiouracil. This compound is used in the investigation of genetic variability of taste perception.

As previously mentioned, the physiology and chemistry and genetics of taste perception is very complex. Briefly, taste perception starts on the tongue and palate, where chemicals within the food stuffs stimulate special epithelial taste receptors that release neurotransmitter substances in response to the chemical interaction of the food/drink (depolarization). This reaction in turn synapses with afferent neurons. Gustatory or taste receptor cells use specific ion channels and receptor sites for transduction. Different taste utilizes different ionic mechanisms or ion channels. Thus, most stimuli (chemical agents that ellicit a response) are water soluble, and therefore are hydrophilic compounds and are dissolved in saliva. A "salty" taste is mediated by monovalent cations (sodium, and potassium), "sour taste is produced by protons (Hydrogen ions), and sweet and bitter are produced by organic compounds (sweet by carbohydrates, bitter by amino acids and alkaloids).

The taste receptors are grouped together (50 -200 receptors) to form a "taste bud". These organized structures are distributed on the tongue and palate and are referred to as papillae of which there are three types; fungiform (mushroom-like), foliate (fin-like on lateral border on the tongue) and valate on the posterior aspect of the dorsum of the tongue (raised, cap-like structures on the back of the tongue). Some older presentations utilize a "taste map" that graphically regionalizes taste on locations on the tongue; these for the most part are incorrect as most taste sensations can be detected throughout the tongue surface.

The three nerves that carry taste perception information to the brain are the chorda tympani (CN VII), which innervates the outer third of the tongue, the glossopharyngeal (CN IX) which innervates the anterior 2/3rds of the tongue, and the superficial petrosal branch of the vagus nerve (CN X) that innervates the glottis and epiglottis.

Now, back to your problem of spontaneous bitter perception. As you can see, trauma or damage to the nerve relaying the taste signal can be altered. That is why I mentioned the idea of injury or infection. Some medications can cause this problem, as can stress. Chemical trauma can also be involved with altered taste perception, either by directly damaging the taste buds or local irritation to the specific nerve.

I would have this evaluated by you primary care doctor and/or dentist. You may need to see an ENT or neurologist for this if it persists.

This problem may also abate and disappear as fast as it presented itself. Treatment is totally dependent upon the etiology of the problem.

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Response by:

Richard J Jurevic, DDS, PhD Richard J Jurevic, DDS, PhD
Formerly, Assistant Professor of Biological Sciences
School of Dental Medicine
Case Western Reserve University