Smell is extremely important in social relations. In some cases, losing smell may well result in losing a job. As many as 20% of the population suffer from impaired smell. COVID-19 patients also lose their sense of smell for a limited period of time. How to regain the sense of smell? In this interview, MUDr. Jan Vodička, Ph.D., a leader of an excellent research team at the Faculty of Health Studies, introduces a unique project involving taste testing in the times of the pandemic, talks about smell therapy and training as well as the relation between the sense of smell and taste.
How many people lose their sense of smell every year?
Approximately 20% of the population suffer from impaired smell, and 5% even lose their sense of smell completely. Many patients do not even realize that they suffer from impaired smell. This is the case, among others, of patients with the Parkinson disease who usually suffer from impaired smell, but rarely undergo an examination.
How important is the sense of smell for us?
Generally speaking, women are much more concerned about any smell impairment. If you work as a chef or wine taster, you may even lose your job if you lose the sense of smell. When we eat, the senses of smell and taste enable us to check the quality of what we eat. Smell may also warn us of the presence of hazardous substances. And its role in social relations is also important. Patients who have lost their sense of smell do not know how their body odour, or cannot join a dinner-table discussion about feed and drink.
Why is it that some COVID-19 patients lose the sense of smell and taste for a short time, while others suffer from the loss for much longer?
A vast majority of patients regain their sense of smell within 4 weeks. Sometimes, it may take longer, most likely due to more extensive damage of the olfactory epithelium.
What should we do if we do not regain the sense of smell even after a month? Should we see a specialist?
It is advisable to see a specialist if the loss lasts for some 4 weeks and there are no signs of recovery. COVID-19 patients usually lose the sense of smell for several days, but sometimes it may take longer. It is not rare that a patient who has suffered from a viral infection takes several years to recover.
Interestingly, many people can smell bad smells after COVID-19. Why is that?
Some 18% of COVID-19 patients who suffer from impaired smell complain of altered olfactory perception. They often refer to bad smells, like the smell of a burning rubber. This is called parosmia. It is based on an assumption that some of the olfactory receptors do not work correctly and the perception is altered. Some studies argue that it may be a case of smell regeneration.
What is the therapy that you offer to patients who have lost smell or taster after COVID-19?
First, they undergo basic examination and their smell is tested using standard methods. We use Sniffin’ Sticks Identification Test and Odourised Markers Test. In addition, we use taste strips to test the sense of taste. In cases of unknown aetiology, we also perform MRI and antibody tests for SARS-CoV-2. The therapy is proposed on the basis of all of these tests.
Is it always the case that if you lose the sense smell, you also lose the sense of taste?
The senses of smell and taste interact very closely. In general, patients with impaired smell usually suffer from mild taste impairment. When people complain of taste impairment, they often say that the food tastes different, which is an important signal for us. In fact, it is often a case of impaired retronasal olfaction.
When you swallow food, the olfactory perception goes from nasopharynx to the nose. That is why smell plays an important role in how we smell and taste food. What we often find out is a situation when patients suffer from a complete loss of smell, but have not lost the taste. That is why we ask patients who complain of altered taste, whether they can smell salty, sweet, bitter and sour taste.
Is it possible to lose only the sense of taste?
Taste impairments not involving loss of smell are extremely rare.
Your current project is called “Telemedicine used for taste testing during the COVID outbreak” You have received funding for the project. Can you tell us more about it?
The aim of the project is to design a self-test for taste testing, which will include testing strips and an app for phones and tablets with an in-built video camera. The app, or rather the software to be more precise, will be used as an interactive manual for self-testing. It will also check whether the self-test has been done correctly and will serves as a tool for collecting data from the patient and determining the result of the self-test. On a voluntary basis, it could also be used for sending the results to the respective physician in an electronic form.
What is the principle behind test strips?
Test strips are used to test for basic flavours – salty, sweet, bitter and sour. Each strip, made either of a filter paper or film, has a layer of the flavour. The patient puts the strip on the tongue and must say what flavour they taste.
What is your relation to the Centre for Technology and Knowledge Transfer?
We cooperate with the Centre and they help us with the commercialization of our work.
Can you describe the cooperation?
It is a case of interdisciplinary cooperation involving the Faculty of Health Studies, the Faculty of Electrical Engineering and Informatics and the Faculty of Chemical Technology. Pardubice Hospital is also involved. In the future, we plan to engage in cooperation with the Interdisciplinary Centre "Smell & Taste” in Dresden and the ENT Department in Geneva. The taste strips tests were developed in Germany and have been used for many years. Our ambition is to make it possible for the patients to self-test and make the whole test more attractive for the patients.
Can the strips reveal that a person is positive for COVID-19?
At the moment, it is no more than a complementary test that COVID-19 patients may undergo. It has no ambition to replace antigen or PCR testing. What it enables us, however, is to determine the functionality of our taste buds. Taste impairments are encountered not only in COVID-19 patients, but also in patients with neurological or metabolic diseases.
You recommend that patients who have lost the sense of smell due to COVID-19 undergo smell training. What exactly is that?
At the moment, it is the only procedure that has been proved to improve our olfactory functions. Twice a day, patients smell four different scents: rose, eucalyptus, cloves and lemon for several minutes. You must do the training for a minimum of six months.
Can smell training work wonders?
The existing studies suggest that it indeed can. My experience shows that it very much depends on the patient’s attitude. Many patients give up after a few days. An active approach is needed for smell training to be effective. It is necessary not to give up.
If the smell training fails, is there any medication that may help?
Oral or intravenous administration of corticosteroids is effective in sinonasal disorders. The good news is that the biological therapy also works. No other drugs have been proved to be effective, and that is why we do not recommend them. We have investigated the effects of vitamins, alpha-lipoic acid, minerals (such as zinc) and others.
Can surgery help to regain the sense of smell?
Surgical treatment only works for patients who suffer from chronic nasal cavity and paranasal sinus pathologies. Endoscopy treatment is used involving the use a camera to treat paranasal sinus.
Patients who have suffered a loss of smell often report that they can remember the taste of certain food mentally. Is it possible?
Absolutely. Smell is closely connected with the memory systems in the brain. Even many years later, a smell can provoke memories of past experience or bring you back to your childhood.
You are a leader of an excellent research team at our university. What is the focus of your research?
Smell-wise, our research deals with how we determine which smells we perceive to be good and which to be bad, as well as respiration in smell stimulation, so called respiration olfactometry. Taste-wise, we aim to find an ideal method for detecting taste impairments. Last but not least, we also deal with hearing and early detection of hearing impairments.
Most common causes of impaired smell
occur after viral upper respiratory infections,
caused by respiratory viruses (respiratory syncytial viruses, influenza viruses), and today mostly by the SARS CoV-2 virus leading to the development of COVID-19
may affect olfactory epithelium that is targeted directly by the virus (e.g. COVID-19), olfactory nerves or centres (herpetic viruses).
occur in oral cavity and paranasal sinus infections, and most often involve a chronic inflammation with the presence of nasal polyps
partially caused by nose blockage where the olfactory molecules are prevented from getting into contact with olfactory epithelium, and partially caused by olfactory epithelium inflammation
occur after head injuries, e.g. falls involving the nape
caused by tearing of nerves in the base of the skull or as a result of contusion (laceration) involving the olfactory systems in the brain