The hand of Dr. Clair Vandersteen wafts a tube of odors under the nose of a blindfolded patient, Gabriella Forgione, during tests in a hospital in Nice, southern France, Monday, Feb. 8, 2021, to help determine why she has been unable to smell or taste since she contracted COVID-19 in November 2020. Credit: John Leicester / AP

My sister-in-law came down with COVID almost exactly a year ago. Vaccines were still unavailable. She works as an EMT and she remembers the exact night when she was exposed while transporting an older patient to the hospital.

Her systemic illness was mild but almost immediately she noticed the loss of her sense of smell and then taste. Coffee, garlic, bacon, red onions and many more foods all smelled awful — not like dirty socks or garbage but a totally new, distinctly COVID-awful smell.

Indeed, there were many new COVID-awful-smells.

She ate because she knew she should and hoped that food would begin to taste better, but it did not. She craved toasted cheese sandwiches because she knew they should taste good — the salt, grease and cheese — but they did not.

It was a long few months until spring.

Finally, she could go to her garden and inhale the scent of lilacs, delighting that they did indeed contain a hint of beauty. The first two bites of a fried egg still tasted nasty, but it grew more palatable from the third bite on.

She asked me as her sympathetic physician relative what I knew about smell, and I realized that I knew almost nothing. So I began to read and ask questions.

There are at least 800 volatile molecules drifting in the air above our morning cup of coffee that create that classic aroma. They waft up into our nose where, like a key fitting into a lock, they attach to a receptor on one of the 20 million olfactory nerves high inside. The impulses are transported up these nerve cells to the olfactory bulb and then to a processing center at the base of the brain.

This is an ancient part of our evolutionary brain. It deals with very basic functions, and connects smell with inputs from taste, sight and even memory and emotion. All this input combines to determine the flavor of what we have eaten.

It is a remarkable system. Our sense of smell determines that there is not just a cup of coffee on the table but that there is also fresh bread, some perfume and clean laundry. Somehow, all this input gets processed and then combined into a whole pleasurable sensation. Change one molecule in coffee and there are those epicureans who can discern the change.

Most often this ability resides in the young more than in the aged. The number of neurons devoted to smell is greatest in youth and decreases with the passage of years, as is the case with hearing, sight and other senses. However, there are exceptions. Elderly sommeliers (wine experts) likely have many more highly developed neural connections than most of us.

Other animals have a different approach. A third of a mouse brain is taken up with smell while a bloodhound — often called a nose with a dog attached — can distinguish smells 1,000 times better than humans.

The nerves that carry these smells from the lining of the nose to the brain are analogous to electric wires. They have an inner conducting core (like the copper wire) and an outer insulating layer of supporting cells (think plastic or rubber). The supporting cells that keep the olfactory nerve cells healthy have basically bored biologists to tears for years — except that now COVID has made them totally unboring.

It turns out that the virus that causes COVID attaches to specific receptors in these support cells; this is where the action is. There are no COVID receptor sites on the nerves themselves, but when the supporting cells become inflamed, the nerves are no longer protected, and the damaged nerves go haywire. It is as if the insulation has been stripped off an electric wire, setting the stage for a massive display of fiery short circuits.

Different researchers have found that the percentage of people with COVID who have altered smell for more than several weeks ranges between 35 and 60 percent. If the infection is very severe it kills off all the support cells, and in perhaps 5 percent of people the nerve dies also, never to return.

With less severe infections the nerve cells regrow but they sometimes “mis-wire” and open up a new pathway. The new sense of smell may be totally different from the old. Coffee may smell like garbage and food like cigarettes. Less horrible, the smell of raspberries may turn into the smell of a flower.

Many diseases are associated with a loss of smell, including other viral infections (rarely the common cold), diabetes and neurological diseases. At this point there is no well documented treatment for the loss of smell due to COVID. There is little data to support the use of antiviral medicines and steroids. Smell training — exposure to four distinct kinds of smells (fruit, flower, spice and herb) two to three times per day for months — is sometimes of benefit.

As always, the best treatment is prevention: get vaccinated, wear a mask, and socially distance!

My sister-in-law is newly aware of the fragility of our senses. She says that now, a year later, she is perhaps “60 percent” better. She was able to smell the turkey at Thanksgiving but unfortunately coffee is still COVID-coffee, not the rich aroma she needs to greet the new day.

Geoff Gratwick is a retired rheumatologist who represented Bangor and Hermon in the Maine Senate from 2012 to 2020. He chaired the Health and Human Services Committee while in the Legislature. He is also...