Imagine waking up one morning after recovering from Covid-19 to find that your coffee smells like unwashed socks, your eggs reek of feces, and your orange juice tastes metallic. Oddly enough, that’s a good thing: it’s a sign that your sense of smell is still working, even if it’s miswired in your brain.
Your ability to smell may also disappear completely, a condition called anosmia. Without warning, you can no longer inhale the sweet smell of your baby’s skin, the roses offered by your partner, or the pungent stench of your gym clothes.
Taste and smell are closely related, so foods can be bland or tasteless. Appetite and zest for life can plummet, which previous studies have shown can lead to nutritional deficits, cognitive decline, and depression.
Danger also lurks. Odorless, you may not recognize the telltale signs of fires, natural gas leaks, toxic chemicals, or spoiled food and drink.
This is the reality for around 5% of global Covid-19 survivors who have now developed long-lasting taste and smell problems, according to a 2022 study. researchers found that around 15 million people may still have problems perceiving smells, while 12 million may have trouble tasting.
Support and advocacy groups such as AbScent and Fifth Sense have stepped up to help, offering affirmation and hope, advice on smell training and even recipes to boost appetite.
Olfactory or scent training encourages people to sniff essential oils twice a day, said Dr. Zara Patel, rhinologist, professor of otolaryngology and head and neck surgery at Stanford University School of Medicine. Medical.
“The way I explain it to patients is that if you had a stroke and your arm didn’t work, you would go to physical therapy, you would do rehab,” Patel said. “That’s exactly what scent training is for your sense of smell.”
As science learns more about how Covid-19 attacks and disrupts the sense of smell, “I think you’re going to see more targeted interventions,” said rhinologist Dr Justin Turner, associate professor of ear, nose and throat. laryngology, head and neck surgery at Vanderbilt University. Nashville Medical Center.
Anyone dealing with a loss of smell and taste “should think positively and assume that their sense of smell will return,” Turner said. “Yes, there are people who won’t get over it, so for those people, we want them to not ignore it. We want them to take this seriously.
People lost their sense of smell and taste centuries ago. Common cold and flu viruses, nasal polyps, thyroid disorders, severe allergies, sinus infections and neurological conditions such as Alzheimer’s disease, Parkinson’s disease and multiple sclerosis can all damage the sense of smell and taste – sometimes permanently.
The same goes for head trauma, exposure to harmful chemicals, cancer treatments, smoking, gum disease, antibiotics, and various medications for high blood pressure, cholesterol, reflux, and blood sugar. allergies, according to the Cleveland Clinic.
Aging is a major cause of loss of smell because the ability of olfactory neurons to regenerate decreases. A study conducted in 1984 found that more than 50% of people between the ages of 65 and 80 suffered from “major olfactory disorders”. The number has soared to more than 75% for people over 80.
When the virus that causes Covid-19 invaded our lives, a relatively rare disease in people under 50 grew exponentially, affecting all ages.
“Covid-19 has affected young people much more than other forms of post-viral smell loss,” said surgeon Dr. Eric Holbrook, associate professor of otolaryngology and head and neck surgery at Harvard Medical School. “You wouldn’t see a lot of smell loss in the pediatric population, for example, and now it’s very common.”
In fact, loss of smell was so prevalent early in the pandemic that it was seen as the canary in the coal mine – an early sign of Covid-19 infection even in the absence of other symptoms.
It is not true today. A study published in May found that 17% of people lost their sense of smell when infected with the Omicron variant, which became the predominant variant of the virus that causes Covid-19 at the end of 2021. (This could still change if the virus mutates.)
In comparison, people sickened by the original two variants, Alpha and Beta, were 50% more likely to lose their sense of smell or taste. Delta was almost as bad – 44% of people were affected, according to the study.
Statistics show that most people recover their sense of taste and smell. An August analysis of 267 people who lost their sense of smell and taste at least two years ago found the majority had fully (38.2%) or partially (54.3%) recovered their ability to smell and to taste. This was especially true for people under 40, according to the study.
But 7.5% had not regained their sense of smell and taste two years after their Covid-19 infection disappeared. Those least likely to recover included people with existing nasal congestion, more women than men, and those with greater initial severity of smell loss, the study found.
How does Covid-19 damage the olfactory system? At first, scientists thought it infected neurons in the nose responsible for transmitting odors from the environment to the brain. These neurons are found in the olfactory bulbs at the very top of each nostril and send axons, or cables, to unique sensory points in the brain.
Soon, studies discovered that the virus does not enter these neurons at all. Instead, it attacks the sustentacular cells, also called supporting cells, which nourish and protect nerve cells from birth. Unlike many other cells, neurons in the nose undergo a rebirth every two to three months.
“Infection (Covid-19) of these support cells probably has some sort of long-term effect on the ability of these neurons to regenerate over time,” Turner said.
“That’s one of the reasons why we sometimes see a delayed effect: people can have smell loss that recovers, and then later they have a second wave of smell loss, parosmia or ‘other symptoms because that regenerative ability is malfunctioning,’ he said.
Parosmia is the medical term for distorted smells, which can often be quite disgusting, Patel said.
“Unfortunately, there are these classic categories of really terrible smells and tastes,” she said. “Sometimes it’s faeces, garbage or old dirty socks. There may be some kind of sickly and sweet chemical smell and taste. Oh, and rotting flesh is another common category.
For many people, parosmia tends to occur or recur after three months, around the time when olfactory neurons would naturally regenerate, experts told CNN.
“If the reconnect misses its target and hits a different place in the brain reserved for a different smell, your sense of smell is going to be totally screwed up,” Holbrook said.
“You have to rely on the ability of those axons to retract and then find their way to the right place,” he added. “Or if they’re not right, wait for those neurons to die and new ones to come back and find the right place.”
Science continues to uncover how the virus attacks. A February study found that it can also damage olfactory receptors on the surface of nerve cells in the nose. These receptors bind odors and trigger nerve impulses that transmit information to the brain.
There may also be a genetic component. A January study found a mutation in two overlapping genes, UGT2A1 and UGT2A2, that play a role in odor metabolism. People with this mutation may be more likely to lose their sense of smell, but more studies are needed to determine the virus. association to genes – if any.
Older people and those with chronic conditions that affect the nervous system, such as diabetes, are often more susceptible to olfactory damage, Patel said.
“It’s the very small vessels in the body, including the nose, that are affected by diabetes, disrupting the flow of blood, nutrients and oxygen to these olfactory nerves,” she said. “People with chronic sinus inflammation or allergies in the nose – anything that makes it harder for our system to bounce back will likely be at higher risk as well.”
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