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I wish we knew more on how covid messed them up and how to fix. Ever since I had covid my smell sensitivity is very low. I get really weird smells and tastes from food that sometimes make me sick.

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If I understand correctly[1] covid messes with supporting cells and not the sensory neurons themselves and there is hope that this means that particular side effect should be temporary.

[1]https://hms.harvard.edu/news/how-covid-19-causes-loss-smell

Unfortunately a new study (not yet peer reviewed) has just come out where they compared the brains of people before and after having covid, and they found "significant losses of grey matter surrounding the olfactory and gustatory system in those that had been infected with severe acute respiratory syndrome coronavirus." So there may actually be neurons involved in smell/taste loss, which isn't great news for the likelihood of these sensations coming back 100%. https://www.news-medical.net/news/20210618/Alarming-COVID-st...

The strange thing for me is that I lost the ability to taste citrus (I can still taste the acidity, but not what makes it good) but gained a heightened sensitivity to other things... I can taste the preservatives in bagged salads and it sucks.

Based on https://news.ycombinator.com/item?id=27570892 seeming reasonable to me, I’m inclined to believe the less sensationalized version of the paper than the breathless headlines that ran.

Probably we are looking at the neurological effects of functional smell loss. On average, this will result in a loss of cell mass in olfactory processing regions. There is no reason to believe this is permanent or something to be alarmed about. The brain is plastic, and it changes in response to use. Not being able to smell well will result in a reduction of resources put towards smell processing. Getting and recovering from covid is depressing (loss of smell is horrible and used to induce depression in mice), and that might explain the general brain-wide trend that's the cause of the breathless headlines.

Probably the olfactory loss continues to some degree for a long time. There may be some nerve damage even if the cells that are targeted by the virus aren't nerves. These then will take a long time to heal. Smells and memories of them seem fixed, but at least in mice, appear to be a flexible entity, with successive exposure to a particular smell causing different patterns of brain activity at every new exposure (https://www.theatlantic.com/science/archive/2021/06/the-brai...) "representational drift" is the key word. This particular system is highly regenerative. It can be damaged easily, and it can recover easily. Not to say that anyone should have to get COVID19.

Study here: https://www.medrxiv.org/content/10.1101/2021.05.28.21257993v...

Fascinating. The implicated gene family matches the subjective experience of the olfactory system damage. Specifically, it seems that while the smells are all "there" (presumably corresponding to intact olfactory neurons), odors associated with complex and toxic sources (e.g. various kinds of smoke) can overwhelm the olfactory system, resulting in a kind of noisy image. A hypothesis the support cells that should be helping to process the odorant molecules are reduced in number and/or efficiency after infection. Some people have more robust UDP glucuronosyltransferase gene copies, helping them to overcome this more easily. This might explain why nasal washes can help some.

You probably get into this in the preprint. I'll have a read before I prognosticate further!

It would be interesting to look at the gene family in the HPRC.

https://www.ncbi.nlm.nih.gov/gene/10941

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