Author: Ellie Wang
Editor: Michael Zhu
Artist: Cici Zhang
At the beginning of the pandemic, you may have first heard of a symptom unique to COVID-19: a partial or complete loss of smell. Why does this happen, and what are the long-term consequences of this symptom?
Firstly, anosmia—total loss of smell—and hyposmia—partial loss of smell—are some of the most reliable indicators of a COVID-19 infection. Sudden smell loss is among the earliest symptoms. According to a study published on the National Center for Biotechnology Information, an estimated 48.47% of people around the world have suffered from anosmia or hyposmia caused by a COVID-19 infection.
After observing this effect, smell scientists suddenly received more attention directed at them and their fields of study than ever before. Their findings reveal that the virus targets and destroys cells within olfactory bulbs—structures containing olfactory sensory neurons that detect smells and cells that support these neurons. These supporting cells replenish neurons and maintain optimal conditions for the bulbs. Therefore, olfactory bulbs would be unable to function without them. Unfortunately, the support cells have ACE-2 receptors that COVID-19 viruses can attach to, granting them access to these important cells. In the process, the cells could become damaged even if a bulb loses some or all of its function.
Finally, what does recovery from COVID-19-caused anosmia or hyposmia look like? One study shows that after the onset, 25% recovered within 14 days and 54.5% recovered within 16-70 days; 20.5% failed to recover after 2 months. Although the majority of people regained their sense of smell, some recoveries were dubious. They experienced conditions called parosmia—incorrect smells—and phantosmia—phantom smells. To this day, scientists are still unsure as to why these long-term symptoms continue, even after testing negative for COVID-19. As for now, no cure exists for anosmia, whether or not it originated from COVID-19.
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