Why do COVID-19 Patients Lose Their Taste and Smell?

For most of 2020, everyone has been told to watch carefully for symptoms of COVID-19: a cough, fatigue, muscle aches, a fever.

All of these are symptoms commonly associated with other colds and illnesses, but many COVID-19 patients suffer from another symptom that isn’t as common: loss of taste or smell. Many people know the medical and scientific reasoning behind the other, more usual symptoms, but why do people who contract this kind of coronavirus often lose their taste and smell?

Well, as you might have expected, the answer has something to do with the nervous system, and also with viral activity in the nasal cavity that happens with many respiratory diseases. Loss of taste and smell isn’t the most common symptom of COVID-19, and not all patients have it, but it is unnerving, and it is important to understand why it happens.

Background Information on Viruses

In order to understand how a virus can make a person lose their taste and smell, you must first understand how a virus gets into a person’s system in the first place. Viruses tend to enter through the nose, and if the hair doesn’t filter out the foreign materials, the particles travel further into the body, until they reach a cell they can enter. Then it all comes down to receptor proteins. Contrary to popular belief, viruses are not actually alive. They rely on the host cell they infiltrate to help them reproduce, and they can’t enter the host cell unless their receptor proteins match the receptor proteins on the host cell. Viruses also sometimes use enzymes to help with this binding process, and this is true with COVID-19.

The Respiratory Effects

As mentioned above, virus particles need to bind to host cells. There are two kinds of cells in particular that COVID-19 binds to often, and they are found predominantly in the nose, throat, and mouth, all areas of the respiratory system. These cells are found in olfactory epithelium tissue and respiratory epithelium tissue. When a virus attaches to these cells in these areas of the body, the immune system activates, which causes inflammation. The irritation can restrict airflow to the nasal cavity, thus blocking off the ability to smell and taste. This symptom of COVID-19 largely has to do with virus cells’ effects on the respiratory system, but it also has a bit to do with the nervous system.

The Nervous System Effects

It would be incorrect to say that loss of taste and smell occurs because of damage to the nervous system; instead, it is more accurate to say that because of the virus’s impact on the olfactory cells and sensors, the information that is supposed to go to the nervous system is not transmitted correctly. The inflammation in the body can affect the olfactory sensory neurons, the neurons that are responsible for bringing information garnered by smelling and tasting to the brain, so it makes sense that these neurons may not function properly until the body clears the virus.

Scientific studies have shown that in most patients, taste and smell come back relatively quickly, so it is likely that these neurons do not die, but are simply rendered useless temporarily. Of course, there are always cases that are more serious than others, but in general, these sensory neurons impacted by the COVID-19 virus will regenerate a couple of weeks after the initial infection. There is still a lot to be learned about the COVID-19 virus, and about the effect it has on the ability to taste and smell. But by continuing to research, we are learning more and more about the illness and the symptoms it causes, and this knowledge will help us get to the end of the COVID-19 pandemic.