Some people who have virus upper respiratory infections have a temporary or permanent loss of taste or smell. In COVID-19, these symptoms appear to be particularly widespread.

More than a year has past since the onset of COVID-19 globally, but for some, these senses are still not restored, and for many who have recovered, the atmosphere has become oddly scented.

In examination of 8,438 people with COVID-19 published last June compiled data that showed 41% smell loss. In another study published in August, a team led by researcher Shima T. Moein at the Institute for Fundamental Sciences in Tehran, Iran, conducted a 100-person COVID-19 smell-identification test in which patients sniffed odors and identified them on a multiple-choice basis. 96% of the participants had some extent of smell dysfunction, and 18% had complete olfactory loss, also known as anosmia.

It is not entirely known how this common airborne virus destroys neurons in the nose, but it has been a subject of widespread scientific inquiry.

Scientists were worried that virus may infect the sensory cells in the nose that send signals to the brain stem. Post-mortem studies of individuals who had COVID-19, however, have shown that the virus rarely reaches the brain.

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Instead the virus is likely to infecte cells that support sensory neurons in the nose—known as suspendicular (sustenance) cells according to a team led by Sandeep Robert Datta. Datta is a neurobiologist from Harvard Medical School in Bostons, Massachusetts.

Whilst scientists know about smelling mechanisms, they do not know how coronavirus affects the taste and chemisthesis. Taste is a feeling that is different from the other sense of smell even as all three attempt to convince us what the “flavors” of foods and drinks might be. Taste relies primarily on taste receptors on the tongue, whereas chemesthesia relies, among other mechanisms, on ion channels on sensory nerves and their response to COVID-19 has not been much studied.

Odor, taste and chemesthesis recover within weeks for most individuals. 72 percent of people with COVID-19 who had olfactory dysfunction reported that they regained their sense of smell after a month in a study published last July, as did 84 percent of people with taste dysfunction.

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The symptoms are more severe for others. Over a long period, some individuals whose senses do not return immediately improve slowly, and this can have consequences, Hopkins says. When a person regains a sense of scent, odors sometimes show a phenomenon called parosmia that is disturbing and distinct from the way they perceive them.

Few proven remedies remain due to a lack of research. But one option is smell training, where individuals regularly sniff prescribed odors to relearn them. Hopkins is partnering with a charity named AbScent in Andover, UK, to get a message out about this instruction to the media. Before the pandemic, there is proof that scent mechanisms of certain individuals with certain impairments can be restored, but they do not seem to work on everybody.