Anosmia: how to find the sense of smell?

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Anosmia is a common symptom in Covid-19 patients. But other factors can also be the cause of loss of smell. Smelling odors or essential oils daily improves, or even restores, lost olfactory abilities.

The Covid-19 pandemic will have highlighted a neurosensory disorder that has received little media coverage, that of the loss or alteration of the sense of smell. In fact, according to a study conducted in 18 European hospitals with more than 2,000 men and women who tested positive for the SARS-CoV-2 virus, 73% of the patients monitored reported a sudden and total loss of the sense of smell (anosmia) and 14% noted a decrease in their olfactory sensitivity (hyposmia), most of the time in association with taste disturbances.

In addition, it is estimated that 10 to 15% of the population already suffered from a more or less severe olfactory disorder before the start of this major health crisis. And here, again, viral diseases (colds, sinusitis, flu, etc.) top the list of culprits, as confirmed by Professor Pierre Bonfils, head of the department of ENT and head and neck surgery at the Georges-Pompidou European Hospital (AP -HP): "These viruses destroy the cells of the olfactory epithelium in charge of detecting the odorous molecules that circulate in the air."

"The second cause of loss of smell is head trauma that can induce a tear in the olfactory nerve that connects the nose to the brain. Not to mention the physiological aging of the olfactory organ since it is estimated that 80% of those over 75 years are affected. "

From nose to brain: how does smell work?

Rose, clove, ginger, coffee extracts. These olfactory stimuli maintain the sense of smell that we know is sensitive to viral attacks and aging.

1. Odorous products enter the nasal cavity. Chewing well also releases a maximum of aromatic molecules in the back of the throat which then pass into the nasal cavity.

2. Smells reach the olfactory epithelium: the chemical message is transformed into an electrical message and stimulates the formation of new sensory neurons.

3. The scent message is transmitted to the scent bulb in the brain.

4. It reaches the amygdala and the hippocampus. The amygdala processes emotion, pleasant or unpleasant, triggered by smell. The hippocampus plays a fundamental role in the memory process. That is why smells are linked to our memories!

5. The olfactory message reaches the orbifrontal cortex, the organ of the perfumer. It is he who deals with the conscious sensations of smell and taste.

Covid-19: Loss of smell and taste can last up to 5 months

Anosmia could sometimes last longer than the Covid-19 infection itself. Because ? "Once the virus is eliminated, the body must replace the olfactory neurons damaged during infection with new ones, generated from a pool of stem cells." But how long does it take to regain this ability? According to a preliminary study by Dr. Johannes Frasnelli of the University of Quebec (presented at the 73rd Annual Meeting of the American Academy of Neurology in April 2021), people with Covid-19 may lose their sense of smell and taste. up to 5 months after infection.

How long does anosmia last?

"Although Covid-19 is a new disease, previous research shows that most people lose their sense of smell and taste in the early stages of the disease," said Dr. Johannes Frasnelli, in charge of the study. The study involved 813 workers who tested positive for coronavirus, who agreed to complete an online questionnaire and take a home test themselves to assess their sense of taste and smell for an average period of five months after their diagnosis, on a scale. from 0 to 10 (the number zero corresponded to the total absence of smell, the number 10 to the returned senses).

It turns out that a total of 580 people lost their sense of smell. And among them, 297 participants, or 51%, said they still had not fully found it five months later. On average, the participants rated their sense of smell as 7 out of 10 after infection, compared to 9 out of 10 before getting sick.

In parallel, 527 of these participants reported loss of taste (ageusia) during infection. 200 people, or 38%, said they still had not regained their sense of taste five months later, while 73 people, or 9%, had a persistent loss of taste with the home test. On average, these people rated their sense of taste as 8 out of 10 after illness, compared to 9 out of 10 before getting sick.

What is Olfactory training?

"Olfactory training is then the best treatment," says Dr. Jerome Lechien of the ENT department at Foch Hospital in Suresnes. The latter followed the cohort of European Covid-19 patients who, for 85% of them, regained their sense of smell after two months. Observation shared by the ENT department of the Saint-Luc University Clinics in Brussels, where this olfactory rehabilitation technique has been recommended for ten years.

"We ask our patients to smell the odors in their homes at least twice a day, for 5 minutes and for two to three months."

"We start the first month with four scents, then we change the following month, says the head of this service, Prof. Philippe Rombaux." We can completely resort to spices, to essential oils. The important thing is to bring together several scents that allow ample olfactory stimulation: fruity, floral, woody ".

This "scent training" relies on neuroplasticity, the brains ability to reorganize itself to compensate for a change or injury. It has the advantage of helping people to regain their sense of smell more quickly and completely, without unwanted side effects unlike corticosteroids (water retention, hypertension, and problems with mood and behavior changes).

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