It is March, 2020. Friends of friends of friends are beginning to contract COVID-19. What is one of the most common symptoms you hear about? The loss of smell. This research article explains how COVID-19 has affected people’s sense of smell, why it’s important to restore this integral sense, and how researchers are working to do so.
Icaro de A.T. Pires recalls when he realized that he had lost his sense of smell: his grape juice tasted flat. Two months after contracting COVID-19, he was unable to smell the beach on his vacation. Distraught by his inability to smell the salt of the sea, he realized how much he valued his sense of smell and its ability to bring up positive memories. Pires, an ear, nose, and throat doctor, recalled a deaf patient who had also lost her sense of smell, but instead of being unable to smell her vacation location, she was unable to smell at work, which was essential for her job at a perfumery.
According to the British Medical Journal, about 5.6 percent of people, six months after having COVID-19, have not fully regained their ability to smell and taste. This is concerning if one considers that about 550 million people have had COVID-19.
SARS-CoV-2 is not the first virus to eradicate people’s sense of smell, but the amount of people who have been affected by it has intensified the need for a solution to smell loss.
The olfactory sensory neurons work similar to the taste bud cells in terms of cell signaling. There are olfactory receptors in the olfactory epithelium (on the roof of the nasal cavity) that detect smells. There are dendrites within these receptors that are covered in cilia. When these cilia are stimulated by odorants that have entered the nose (in a G-protein-coupled receptor process), this depolarizes the olfactory receptor cells and sends electrical signals to the olfactory bulb, which are tied to the olfactory epithelium by axons, making the olfactory bulb the postsynaptic cell. These then send the signal to the brain that a scent has been received.
The olfactory sensory neurons are vulnerable to mucus, bacteria, and viruses that might inhibit their ability to work. Recent studies show that SARS-CoV-2 indirectly affects the olfactory system by killing sustentacular cells that support olfactory neurons. This attack harms the olfactory epithelium, causing the neurons to receive less odor molecules. Over time, the inflammation that effects the olfactory sensory neurons decreases, but for some people recovering from COVID-19, it can take up to months for them to regain their sense of smell.
Researchers are exploring smell training, a process by which a participant smells four different smells 30 seconds each, twice a day for about three months. Generally, smell training seems to work, with about 30-60% of people having improved senses of smell after completing the training.
The process requires discipline and endurance: taking even one day off can undo your weeks or months of progress. However, this is counteracted by the fact that there are no negative side effects, with the exceptions of frustration for those it does not work for. Doctors want to warn their patients about the possibility that, despite one’s dedication to smell training, it still might be unsuccessful in restoring your sense of smell.
Researchers are not completely sure how smell training helps, but they have ideas of some possibilities. It is possible that the training stimulates growth of replacement olfactory cells, or it possibly strengthens pathways in the brain. There is also data that shows that smell training boosts the amount of olfactory sensory neurons; however, is unclear exactly how smell training works.
There are other possible solutions to help restore one’s sense of smell, such as steroids, supplements, or more advanced solutions such as epithelial transplants.
The article explains how that people do not recognize the importance of their sense of smell until it is gone. In fact, in a survey done on 400 people, 19% percent said that they would rather give up their sense of smell than their cell phone. Would you rather give up your sense of smell or your cell phone? What about giving up your sense of smell or your little left toe? 15% percent of people said that they would rather give up their sense of smell over their little left toe.
Researchers are continuously researching solutions to restoring people’s sense of smell. People who have lost their sense of smell for an extended period of time from COVID-19 are struggling with their ability to live their lives to the fullest-they want to wake up and smell the roses, but they cannot.