One of the most curious symptoms of COVID-19 is loss of smell. It can occur during the illness and linger for weeks, months or years. It can also crop up after the infection goes away. This makes loss of smell a common symptom of long COVID-19.
Long COVID can affect vaccinated or unvaccinated individuals, regardless of the severity of infection. Our understanding of long-COVID is still evolving, and scientists and doctors are studying the individual symptoms and how to support people affected by them.
Loss of smell, even temporarily, was one of the primary indicators of a COVID-19 infection early in the pandemic.
“Millions of people around the globe have suffered this symptom during the pandemic,” said Dr. Timothy Smith, ear, nose and throat specialist at Oregon Health & Science University. “We found that probably 80% of those patients who have a loss or distortion of their sense of smell will recover that sense about one to three months after the COVID-19 infection has resolved. But that still leaves up to 20% of people who have an ongoing disturbance in their sense of smell.”
Dr. Smith has spent decades treating patients who lost their sense of smell due to viral illnesses. He says the symptom falls into one of three categories: 1 – total loss (anosmia), 2 – partial loss (hyposmia) or 3 – distorted sense of smell (parosmia).
How smelling works
The smelling process begins at the base of the skull, where the skull bones meet the nasal cavity. The skull bone contains nerve fibers called olfactory nerves, which sit at the top of the nasal cavity and receive air, along with any scented molecules the air carries. These molecules get funneled up the nose into the narrowest portion of the nasal cavity. From there, the olfactory nerves are stimulated, sending information to different regions of the brain for processing, such as those that deal with emotions or memory.
“Many people have had the experience of smelling something over the holiday season that reminds us of our childhoods. But we’re really in our infancy of understanding all the communications that occur within this neural network in our brain,” Smith said.
Our sense of taste is closely tied to our sense of smell. While they have different nerves, a portion of our “taste buds” activate when a food’s flavor bypasses the palate and goes into the nasal cavity, where it gets processed by the olfactory nerves.
COVID-19’s impact on olfactory nerves
“The SARS-CoV-2 virus might not affect the olfactory nerves directly,” Smith said. “There’s some good evidence showing the virus might injure the supporting cells around the nerves. If the supporting cells that provide nutrition to the nerves are injured, the olfactory nerves themselves may be secondarily injured.”
Nasal or sinus congestion (swelling) during the early stages of a COVID-19 illness also prevents smell molecules from getting where they need to be—the narrowest point in the nasal cavity— to be sensed. By the time the swelling caused by congestion goes down, the damage to the olfactory nerves may be done.
The mental impact of loss of smell varies, but in some cases can be extreme. Lack of sensory input from smell can dull the world around you. And some people may not lose their sense of smell, but rather their sense of smell gets distorted. When that happens, otherwise normal odors can smell terrible to them, making it difficult to enjoy food or everyday experiences.
“The most common distortion I hear in my clinic is one of smoke,” Smith said. “Imagine smelling a grapefruit, but it smells like smoke. Sometimes, nice-smelling things can smell like rotting trash, and that can be really disruptive to someone’s quality of life.”
Another concern for those who have lost their sense of smell is safety. Our sense of smell helps keep us safe, in ways we may take for granted. For example, Dr. Smith advises patients to make sure they have working smoke and gas detectors. Rotten food smells bad, warning us not to eat it, so people who have a compromised sense of smell should take extra care to check expiration dates on their food.
Treatment
Medical treatments for smell loss or distortion are still in development, but anyone can practice smell training therapy at home.
“Smell training therapy is not invasive, relatively inexpensive and has probably the best evidence behind it,” Smith said. “It consists of spending a few minutes each day, a couple of times a day, smelling two or three or even more essential oils. It’s like physical therapy that you might have after a knee operation or a hip replacement: going back to the basics and retraining those muscles to develop the coordination and strength around the impacted area. The same thing appears to be true with these olfactory nerves as they become injured.”
No particular essential oil is more effective in therapy than others. What’s important is stimulating the olfactory nerves, so choose oils with scents you enjoy.
Working to retrain your nerves takes time but is the easiest way to see results. Most guidance recommends starting with three or four essential oils, smelling one for 10 seconds, pausing for 10 seconds, and moving the next. Repeat this process twice a day.
Dr. Smith would take it a step further.
“I’d smell cinnamon and think or say to myself, ‘This is what cinnamon smells like,’ just to try to get all of those connections working again.”
The longer someone experiences smell loss or distortion, the more challenging it can be to reverse. Dr. Smith recommends patients seek care and start at-home smell training therapy soon after their sense of smell has been affected.