Symptom of loss of taste can vary from complete loss to partial loss. It can also be temporary or permanent, though the latter is very rare. Again the loss can be in certain segmental sections of the tongue depending on a particular nerve pathways that is affected. It is not unusual to have altered taste when we have ‘fever’ or have a ‘gastric upset.’
The sensation of taste can be categorized into five basic tastes: sweetness, saltiness, bitterness, sourness, and umami.
The tongue is divided into zones for different types of tastes. For example sweet and salty tastes are located in the front and at the tip of the tongue whereas the sour taste is located on the side and bitter at the back.
Do You Have a Taste Disorder?
Do you have a problem with your taste? If you do, then you need to answer the following questions:
• Have you recently had cold or flu?
• Have there been any changes in sense of smell?
• Do you take any medications and if so the names and the dose and for the condition they are being prescribed?
• What changes in taste have you noticed and for how long?
• Do all foods and drinks, sweet or sour, taste the same?
Taste disorders are classified depending upon the degree and variation of loss of perception of taste into these broad category -
a. Phantom taste perception: This is the most common of the taste disorders. The person has a unpleasant taste even though there is nothing in the mouth.
b. Reduced ability to taste the five tastes - sweet, sour, bitter, salty, and umami. The condition is called hypogeusia [hy-po-GYOO-zee-a]
c. Altered taste where the patient experiences metallic, salty, rancid or foul taste- Dysgeusia [dis-GYOO-zee-a]
d. Complete loss of taste - Ageusia[ah-GYOO-zee-a]. This is rare; usually there maybe loss of smell and not taste.
Loss of taste usually occurs in combination with loss of smell. Also, in certain cases, loss of smell is often perceived as loss of taste due to their close relation. There is loss of taste buds as we age and a 70 year old has only 15 to 20% taste buds of a 20 years old.
Nerves are like thin cables that carry sensation from the periphery or the surface of the body to the brain and carry commands from the brain or spinal cord for any action that is required. Taste buds sense the taste in the food, the signals of which are transmitted to the brain via nerves where the taste sensation is perceived. Thus, a problem in either the taste buds, nerves supplying the taste buds or the brain can result in loss of taste.
Conditions with loss of taste that occur commonly are discussed below:
1. Age and Loss of Taste - We lose taste as we age and the order in which taste is lost is usually first for sweet then for salty items followed by bitter or sour.
Sweet → Salt → Sour → Bitter
2. Upper respiratory infection - The loss of taste in this condition is usually transient or temporary. It usually occurs immediately after an episode of upper respiratory infection. Chronic middle ear infections are also associated with loss of taste sensation. An upper respiratory infection can be diagnosed though patient history and physical examination.
3. Glossitis - Glossitis or inflammation of the tongue results in loss of taste buds, giving rise to loss of taste. Anemia due to vitamin B12 deficiency and iron deficiency are common causes of glossitis.
4. Medications - Commonly used medications can cause varied degree of taste disturbances. Usually, no treatment is required. Dosage modification or discontinuation of the drug causing this problem usually resolves the issue. Some of the medications that cause taste disturbance include -
• Antifungals, (terbinafine),
• Antimicrobial drugs (metronidazole)
• ACE inhibitors (captopril)
• Chemotherapy (cyclophosphamide, cisplatin, etoposide)
• Antibiotics (tetracyclines)
5. Tonsillectomy - Loss of taste sensation of variable degree is noticed after tonsillectomy surgery. Chemical testing reveals reduced taste sensation on the posterior third of the tongue.
6. Bell’s palsy - Bell’s palsy is a condition that results in paralysis of one side of the face. Patients might experience sudden loss of taste along with the paralysis, Evoked electromyography and chemical gustometry are useful in confirming the diagnosis.
7. Sjogren’s syndrome - Reduced taste perception occurs with other symptoms like problems with swallowing, dry skin, eyes and mouth, and painful joints. Tests like Schirmer test (which shows reduced tear production), slit lamp examination of the eye (which reveals kerato-conjuntivitis sicca) and biopsy of the salivary gland are useful in confirming the diagnosis.
8. Trauma - Trauma to the head and neck region can alter taste sensation. It could arise due to radiation treatment to the head and neck, surgeries in the head and neck, dental procedures, head injury etc. A history of the underlying condition is usually available.
9. Cancer - Cancers of the mouth could affect taste sensation. Cancers of the oral cavity damage the taste buds leading to loss of taste. In general, any cancer being treated with chemotherapy drugs leads to changes in taste due to damage to the oral cavity, salivary gland dysfunction and infection in the oral cavity.
10. Digestive tract disorders - There are various digestive tract disorders like reflux disease (GERD), gastritis and gastroenteritis that can cause taste disturbances. GERD causes bitter/sour taste due to back flow of stomach acid and juices into the esophagus, while gastroenteritis causes ‘metallic taste.’
11. Neurological disorders - Patients with neurological conditions like multiple sclerosis, Parkinson’s syndrome, Alzheimer’s disease etc. experience change in taste / reduced taste perception. This happens due to damage to the brain tissue in area of taste recognition like thalamus, cranial nerves etc. MRI Scans are helpful in confirming the cause for taste disorders.
12. Diabetes mellitus - Taste disorders are common in patients with poor blood sugar control. This is due to complications that arise due to poor sugar control such as periodontitis, gingivitis, bacterial/fungal infections, stomatitis, salivary dysfunction etc. Henkin’s test is useful in confirming the diagnosis.
13. Smoking - It affects the shape and functional ability of taste buds there by causing taste disorders. However, the number of taste buds is not affected by smoking. Quitting Smoking decreases the intensity of damage to the taste buds, as well decreases the risk of cardiovascular diseases, cancer etc.
14. Kidney disorders - In chronic renal failure patients, taste disorders are due to fewer fungiform taste buds. Also excessive urea in the body leads to change in the perception of taste of food and bad breath leading to loss of appetite and unintentional weight loss.
15. Other causes - There are a number of other conditions which can cause taste disturbances like Cushing’s syndrome, Hypothyroidism, Niacin/Zinc deficiency, Familial dysautonomia etc
Tests for the diagnosis of loss of taste
Loss of taste is assessed with examination, history taking and investigations. Examination includes physical examination of ear, nose and throat along with dental examination and assessment of oral hygiene. Investigations include:
• Sip, spit and rinse test
• Tests to determine response to different concentrations of a substance
• Tests to recognize lowest concentration of a substance
• Tests to compare the tastes of different substances
Apart from the above tests depending upon the medical history additional investigations might be required like X-ray, CT scan head and neck etc. to rule out causes of loss of taste in the brain.
Frequently Asked Questions1. Which specialist doctor should be consulted for Loss of Taste?
You should consult an ENT specialist or a General Physician
2. Which is the most common pure taste disorder?
The most common pure taste disorder is phantom taste. It is perceived as a bad taste in the mouth.
Latest Publications and Research on Loss of TasteHuman Pathogenic Paecilomyces from Food. - Published by PubMed
Taste and odor preferences following Roux-en-Y surgery in humans. - Published by PubMed
Eosinophilia and systemic symptoms with transient ageusia: a drug reaction caused by zonisamide. - Published by PubMed
Engineered Hsp70 chaperones prevent Aß42-induced memory impairments in a Drosophila model of Alzheimer's disease. - Published by PubMed