- Loss of smell (anosmia) is a common symptom of COVID-19, in fact, it occurs more frequently than fever or respiratory symptoms.
- The researchers found that in COVID, as with other viral infections, loss of smell is related to the way the virus attacks cells in the back of the nose.
- The lost sense of smell can return slowly after an illness, but for some people it may not return completely, or at all. When the sense of smell returns, things that are supposed to smell good can smell bad at first, a condition called parosmia.
One of the signs of COVID-19 infection is loss of smell (anosmia). This is the main neurological symptom of COVID, affecting approximately 90% of patients with this virus. Experts say that loss of smell may better predict COVID infection than other symptoms of the disease.
What does it mean if someone with COVID or another viral infection loses their sense of smell? Will he come back? And if so, will everything be as before?
Viruses and odor
Eric Holbrooke, MD , assistant professor of otolaryngology and head and neck surgery at Harvard Medical School and chair of the rhinology department in the Massachusetts Department of the Massachusetts Ophthalmology Clinic, tells Get Meds Info that viruses other than COVID can cause anosmia.
"Post-viral odor loss was a well-known phenomenon," says Holbrooke. "We were not able to directly determine which virus caused this, mainly because these patients came in long after the acute symptoms and therefore it is very difficult to determine which virus actually caused this."
People can lose their sense of smell if they have a stuffy nose from a cold or the flu. While this may be temporary, some people will notice that their sense of smell has not returned after the nasal congestion has cleared up.
Holbrooke specializes in treating smell and taste disorders and says that "about 40% of the patients who came to me had a history of colds and then loss of smell." People can also suddenly lose their sense of smell after a head injury.
Coronaviruses other than SARS-CoV-2 can also cause loss of smell. Holbrooke says that anosmia has been reported in some cases of the coronavirus that caused an outbreak of severe acute respiratory syndrome (SARS) in 2003 and 2004, but the symptom "was not as common as with COVID-19."
European researchers found that 86% of a group of 417 mild to moderate COVID-19 patients lost their sense of smell. A second, larger study found that 87% of 2013 mild-to-moderate COVID-19 patients lost their sense of smell.
Holbrooke says the researchers were "a little informed" about COVID-19 because loss of smell was reported early in Europe, which was hit by the pandemic in the United States.
"If you have a normal sense of smell and you suddenly lose it, you really notice it," says Holbrooke. "The combination of smell and taste is what gives food its flavor."
People who experience a progressive loss of smell, which can occur with age, may not be as concerned because the gradual loss allows them to get used to the change.
Although some people with COVID-related anosmia recover within a few weeks, many people may take longer to recover. One study found that about 95% of people recover from COVID-related anosmia within six months.
What Causes Loss of Smell?
The structures that make up the sense of smell are located in the upper part of the nasal cavity, behind the nose, just in front of the brain. Olfactory sensory neurons detect molecules in the air that bind to substances around us and then directly to the brain. Smells reach neurons both through the nostrils and through the mouth.
Eric Holbrooke, MD
If you have a normal sense of smell and suddenly lose it, you really notice it. The combination of smell and taste is what gives food its flavor.
– Eric Holbrook, MD
When the coronavirus began to affect patients' sense of smell, the concern was that neurons were affected, suggesting that other neurological problems could be occurring.
Sandeep Robert Dutta, MD , professor of neuroscience at Harvard Medical School, tells Get Meds Info that what actually happened was that the sense of smell was disrupted by SARS-CoV-2 when it attacks the cells that support cells. neurons in the nose (which senses it smells) rather than an attack on the sensory neurons themselves.
Dutta and his colleagues found that sensory neurons lack a receptor protein called ACE2 (which the SARS-CoV-2 virus uses to enter human cells). However, the cells that support neurons contain proteins, so the virus can attack them.
Holbrooke says the study suggests that impaired smell and the association of loss of smell with COVID-19 are likely related to inflammation that occurs around sensory neurons, but does not necessarily directly infect them to cause damage.
Why does it smell strange after COVID?
Since sensory neurons are not affected, the loss of smell that can occur with COVID is unlikely to be permanent. Olfactory sensory neurons and other cells can grow back, which Holbrooke says means that unlike vision or hearing loss, the sense of smell can be restored.
However, when restoring the sense of smell, which does not always happen, there may be mistakes. Nerves grow slowly and must reconnect with the brain, and these new connections can have a period of overload during which they do not function properly.
Holbrooke says that parosmia, when what you smell like an odor doesn't match the actual smell, can also occur. For example, the scent of a rose is ultimately perceived as the scent of a skunk. Interestingly, the wrong feeling is often more bad than good – a rose can smell like a skunk, but not the other way around.
What does this mean to you
If you have been sick with COVID and have lost your sense of smell, be aware that this symptom is very common. While for some people the sensation recovers within a few weeks after recovery, for others it may take longer, and as the sensation returns, the odors may be felt in an unusual way for a time. In some cases, the loss of smell is irreversible.
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