Q: I have had no sense of taste since December and a coating on my tongue. I've not been ill, and my doctor hasn't a clue what's going on. I am 72.
Mrs C. Hemp, Ruislip, Middlesex.
A: I understand why you feel anxious: an impaired sense of taste and smell are common symptoms of Covid-19.
However, you have experienced this issue since before the arrival of the virus in the UK and you have no other Covid symptoms.
The technical term for partial impairment of the sense of taste is hypogeusia. A complete absence is ageusia, and this is far less common. You don't clarify which you have, so I will opt for the probability that it is hypogeusia. Taste involves the stimulation of taste receptor cells and the subsequent transmission of signals to the brain.
The cells are located on taste buds on the tongue and elsewhere in the mouth, and this area is served by three different major nerves. This is why complete absence of the sense of taste is rare because multiple nerves are involved — damage to all three is unlikely.
An impaired sense of taste and smell are common symptoms of Covid-19. Stock image
However, there are other possible causes. Infections and inflammatory problems such as gingivitis (gum infections) or candidiasis (oral thrush) may lead to changes in the chemistry of your saliva or the mucus surrounding the taste buds, making them less sensitive. Another cause is an inflammatory disorder, such as Sjögren's syndrome (a disorder of the immune system that leads to dry eyes and dry mouth), which may cause closure of the taste pores through which molecules access the taste receptors.
Another cause is vitamin B12 deficiency, which results in atrophic glossitis, when the taste buds — the tiny doorknob-like protrusions on and around the tongue — become worn away. That's because these cells have a high turnover and the vitamin plays an important part in the renewal process.
There are a number of drugs that can interfere with the taste sensation, too; ACE inhibitors for blood pressure are an example. But you say in your longer letter that you don't take medication.
Being deficient in the mineral zinc (as can occur due to malnutrition, Crohn's disease, kidney failure and liver disease) is also a cause of altered taste sensation — but you say you're in excellent health.
Diminished taste may also occur with advancing age: one study in