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How coronavirus affects smell

How Covid-19 affects the olfactory system.

AbScent Presents was grateful to Dr Nancy Rawson, Vice President of the Monell Center in the USA, and Dr Federica Genovese, a post-doctoral researcher at the Monell Center for sharing their understanding of how Covid-19 affects our olfactory system.

They explained why some people are still unable to smell normally for many months after they had the virus, and why you shouldn’t lose hope for a recovery.

How the nose works

The area of tissue in our noses that detects the many thousands of molecules that make up a smell is called the olfactory epithelium. Olfactory neurons within this tissue detect odour molecules and turn them into messages that are fired to the olfactory bulb where the brain interprets them as smells. One smell may need thousands of neurons acting at the same time to send a complete picture to the brain. 

Olfactory neurons are kept in place by a tissue of support cells that provide the right environment to keep them healthy and functioning. It’s these support cells that are affected by Covid-19.

Under attack

For viruses to get into the body they need a specific chemical to be present on the surface of the cell they want to attack. In the case of SARS-CoV-2 - the virus that causes Covid-19 - this chemical is called ACE2. ACE2 isn’t on olfactory neurons, but it is found on the support cells.

It appears that the virus is attacking the support cells, and without them, the olfactory epithelium loses its structure and the olfactory neurons can’t work properly. If the neurons aren’t getting the support they need, they can’t send effective smell signals to the brain, and you lose the ability to smell normally. 

The good news is these support cells can regrow and the olfactory epithelium can heal. But while this healing process is going on, the smell messages that reach the brain are affected. This could mean you smell nothing (anosmia), you smell the wrong thing (parosmia) or you might even smell something that’s not there at all (phantosmia).

Healing from an injury

Understanding how our olfactory epithelium has been injured by Covid-19 helps us to think sensibly about the healing process. Whenever you have an injury, it takes time to heal, and this delicate structure in the nose can take many months before it starts to work properly.

Smell training helps the recovery process because it’s like physiotherapy. Gentle and regular exercise will help the injury to heal, but it’s not going to be a quick fix. 

Watch the webinar

This is just a short summary of Nancy Rawson and Federica Genovese’s talk. Watch the full webinar on our YouTube channel.

December 23, 2020