Covid-19: loss of smell and taste

Loss of taste due to Covid.

© Shutterstock

Loss of taste due to Covid.

Loss of taste due to Covid.

© Shutterstock Covid-19: loss of smell and taste The loss of the sense of smell and taste is one of the most common side effects of a Covid infection - and a disaster, especially for chefs and sommeliers. But why does this disorder develop?

»From one day to the next, I could no longer smell or taste anything,« says Benjamin Edthofer, who caught an omicron infection at the end of January. Especially bad in his case: Edthofer is a sommelier at the wine bar Heunisch und Erben in Vienna’s third district. »I didn't actually have any symptoms. I wasn't sick,« Edthofer recalls, »but I suddenly couldn't distinguish four completely different wines by smell. All four smelled completely the same to me, or rather, they smelled like nothing at all.«

Total loss of smell

What is bad for anyone turns out to be a disaster for someone who has to have a functioning olfactory system for professional reasons. Edthofer: »In the beginning, I only perceived odours five percent of the time. I could hang up my job with that. Fortunately, it got better from week to week. I estimate that my sense of smell has now returned to 60 percent. But I still can´t smell as well as I could before.«

In such a case, doctors speak of anosmia. A distinction is made between functional and complete anosmia. In functional anosmia, the sense of smell is so severely impaired that it can no longer be used meaningfully in everyday life, even if a few odours can still be perceived occasionally, faintly or briefly. However, this residual ability to smell is insignificant. In the case of complete anosmia, the sense of smell is completely disabled, which means that there is no residual ability to smell.

Whether functional or complete anosmia, the everyday experience of those affected is simply: »I can no longer smell.« So no more asking your nose whether the milk is sour, the T-shirt from the day before is smelly or the perfume gift from your partner is good or disgusting. In addition, many people with anosmia have problems with their sense of taste: most of them can taste salty, sour, sweet and bitter things normally, but can no longer distinguish between certain flavours. This requires not only the taste receptors but also the olfactory receptors on the tongue; only when they work together can a flavour fully unfold.

But how do such disturbances in the sense of smell occur? Two types of receptors play an important role: the ACE2 receptors (angiotensin-converting enzyme 2) and the neurolipin-1 receptor serve the Covid viruses as an entry port into the sensitive cells.

A particularly high density of neurolipin-1 receptors is found in the human nose in the olfactory epithelium. Researchers have now discovered that coronaviruses can even penetrate the brain. In this way, virus particles could reach the central nervous system since there is a direct connection to the brain via the olfactory epithelium. Whether the viruses take this direct route via the olfactory epithelium and to what extent this transport route is suppressed by the immune system in most people has not yet been proven.

By the way, smell and taste disorders can also occur during influenza, but the mechanisms are different. In the case of influenza or flu-like infection, the patients have a cold, their nose is swollen shut and when the fever is gone, some lose their sense of smell for a short time, which then quickly returns. Covid patients are different: they can usually breathe very well through their nose but cannot smell from the beginning of the infection.

Interestingly, the olfactory system is also the only sensory system where the sensory cells are neurons, while the gustatory system is made up of skin cells, mainly on the tongue. It seems that the neurons in the olfactory system die off during a Covid infection. Fortunately, the neurons in the olfactory system can renew themselves, but this can take several months.

What therapies are available?

And what can be done about long-term smell and taste disorders? Researchers at the University of East Anglia in the UK looked into this in a recent study and concluded: Not only medication but above all intensive olfactory training helps Long Covid patients, which is why more and more experts recommend structured olfactory training for post-infectious olfactory disorders. The exact structure of the training can vary and is discussed with the patient in each case. For example, the patient can sniff twice a day for several weeks at olfactory training sticks that contain a certain scent (e.g., lemon, clove, eucalyptus).

This training of the sense of smell can be supported by associating each smell with pictures or words. When sniffing the lemon pen, for example, patients can look at the picture of a lemon and say the word lemon in their mind or out loud. In this way, the olfactory impression is better remembered. However, it is still unclear whether the sense of smell recovers 100 percent in all patients.

Especially in short pieces, watch out for the tendency to repeat vocabulary items, especially ones that are not needed at all. In this case, the word 'so-called' is not needed. Although one of its meanings is 'commonly named', it is not needed when we are simply stating the name of something, particularly its scientific name. Further, the word also means 'falsely or improperly named', and this negative connotation can come to people's minds when the word is used where it is not needed.