Anosmia is a common symptom in patients with Covid-19. But other factors can also be the cause of a loss of smell. Smelling odors or essential oils on a daily basis improves, or even regains, lost olfactory capacities. Update on the olfactory training methods to follow.
The Covid-19 pandemic will have brought to the fore a neurosensory disorder little publicized until then, that of loss or impairment of smell. Indeed, 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 patients monitored reported a sudden and total loss of their 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 smell disorder more or less severe before the onset of this major health crisis. And again, viral diseases (colds, sinusitis, flu, etc.) are at the top of the list of culprits, as confirmed by Professor Pierre Bonfils, head of the ENT and head and neck surgery department at the Georges-Pompidou European Hospital (AP-HP): “These viruses destroy the cells of the olfactory epithelium responsible for detecting the odorous molecules circulating 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 over 75 years are affected. ”
From nose to brain: how does smell work?
Extracts of rose, clove, ginger, coffee … These olfactory stimuli maintain the sense of smell which is known to be sensitive to viral attacks and aging.
1. The fragrant products enter the nasal cavity. Chew well also allows to release a maximum of odorous molecules in the back of the throat which then pass into the nasal cavity.
2. The odorants 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 the emotion, pleasant or unpleasant, triggered by the smell. The hippocampus plays an essential role in the memory process. This is why smells are linked to our memories!
5. The fragrant message arrives at orbifrontal cortex, the perfumer’s organ. It is he who deals with the conscious sensations of smell and taste.
The anosmia could sometimes last longer than the infection with Covid-19 itself. Why ? “Once rid of the virus, the body must still replace damaged olfactory neurons during the infection by new ones, generated from a stock of stem cells “, explains Inserm on its site. But how long does it take to recover this faculty? According to a preliminary study led by Dr Johannes Frasnelli of the University of Quebec (presented at the 73rd annual meeting of theAmerican 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 most people lose their sense of smell and taste early stages of the disease“Says Dr Johannes Frasnelli, in charge of the study. The study involved 813 workers who tested positive for the coronavirus, who agreed to complete an online questionnaire and perform a home test themselves to assess their meaning. taste and smell over 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 returned senses).
It turns out that in total 580 people have 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, participants rated their sense of smell as 7 out of 10 after infection, compared to 9 out of 10 before they got sick.
At the same time, 527 of these participants reported a loss of taste (ageusia) during infection. 200 people, or 38%, said they still did not have 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 becoming ill.
“Discover the extent of the associated neurological problems”
“Our results show that an alteration in smell and taste can persist in a number of patients. the importance of following up infected people and the need for further research to uncover the extent of neurological problems associated with Covid-19, “concludes Dr Johannes Frasnelli.
Loss of smell can drastically impair the quality of life and has repercussions on the way we eat, social relations and even the perception of certain dangers.
In France, people who experience a drop in smell related to Covid-19 are invited to advance work in this area by responding to an online survey designed by a team from the Lyon Neuroscience Research Center.
Olfactory training, the best treatment to regain your sense of smell after Covid-19?
Corticosteroids in the form of tablets or spray, usually intended to treat anosmia, are contraindicated if it is due to Covid-19.
What does the olfactory training consist of?
“Olfactory training is then the best treatment, “said Dr Jérôme Lechien from the ENT department of 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. Report 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 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 smells, then we change the following month (s), specifies the head of this service, Prof. Philippe Rombaux. Some patients have used board games such as “Loto des odeurs” or “Le nez du vin”. But we can completely turn to spices, essential oils. The important thing is to bring together various smells allowing a broad olfactory stimulation : fruity, floral, woody … ”
This “odor training” is based on neuroplasticity, the brain’s ability to reorganize itself to compensate for a change or injury. It has the advantage of helping people recover their sense of smell faster and more completely, without unwanted side effects. unlike corticosteroids (fluid retention, hypertension and problems with mood swings and behavior).
A 12-week olfactory rehabilitation program using essential oils
An olfactory rehabilitation protocol from essential oils was developed by Jean-Michel Maillard, traumatic anosmic, founding president of the association anosmie.org, in collaboration with the neurobiologist and director of neuroscience research at CNRS, Hirac Gurden.
“We were based on previous work which showed that 40% of people who performed the complete protocol had better sensory acuity”, recalls Hirac Gurden. On the program: lemon extracts (lemongrass), from clove (eugenol), of pink (phenylethanol),eucalyptus (eucalyptol), to which we can add two additional odors: the pepper mint and the coffee bean.
These essential oils that are dosed at 2% (20 drops in 50 ml of water) are to smell blind, twice a day and for 12 weeks. The outcome largely depends on the severity of the disorder. “Thanks to this daily training, I can detect ten odors, and identify four: coffee bean, peppermint, eucalyptus and rose”, specifies Jean-Michel Maillard.
When one suffers from loss of smell, the primary objective is not to put words into a smell, but to regain sensory detection, and then, to try to identify it.
Hirac Gurden advises to repeat this daily training at regular intervals: “As soon as you feel that your olfactory sensitivity decreases, you restart the daily stimulation sessions. At the same time, be sure to inhale the smells that surround you, in the kitchen or in the classroom. of a walk in the forest, for example. The more olfactory stimuli you receive, the more you will increase and preserve your sensory acuity. ”