L’hyposmie is a symptom that is characterized by a decrease in smell. This can become very disabling on a daily basis. Its prevalence increases with age. What are the causes ? What are the consequences ? Who to consult? Is it curable? 

Hyposmia is the partial loss of smell. 6% of French people suffer from it, which represents 4 million people in France. This is a qualitative and / or quantitative alteration of the sense of smell.

The prevalence of olfactory disorders increases from the age of 50 to reach 20% of the population after 65 years, and 80% after 75 years. Men are more affected, since they are 25% to be affected after 65 years, against 16% for women over 65 years. Odor disorders are also more frequently observed in patients with Alzheimer’s disease since they are found in 80% of them.

There are multiple possible causes responsible for hyposmia. Here are the main ones:

• viral infections such as the common cold, sinusitis or the flu: in fact, certain viruses can destroy, during the acute phase of the infection, the cells of the olfactory epithelium responsible for detecting the odorous molecules circulating in the air and transmit them along the olfactory fibers to the olfactory bulb. The loss of smell following a viral rhinitis affects, in particular in 60% of cases, women from 50 to 65 years. In this case, the sense of smell often returns in 1 to 3 years, the time that the olfactory epithelium renews itself;
• nasal polyposis: it is a congestion of the nasal cavities by polyps. This affects 3 to 4% of adults;
• head trauma: in this case, the smell disturbances can be due to a hematoma and can disappear in 3-4 months, or to a tear in the olfactory nerve that connects the nose to the brain;
• presbyosmia, that is to say the degradation of olfactory functions with age: over the years, the nasal mucous membranes dry up. The molecules responsible for the perception of odors then have more difficulty in clinging to them;
• COVID-19: olfactory disorders are indeed prevalent in patients with a mild to moderate form of coronavirus disease 2019;
• neurodegenerative pathologies such as Parkinson’s disease, multiple sclerosis or even Alzheimer’s disease;
• herpes;
• the allergies ;
• kidney or liver failure;
• occupational exposure;
• tobacco consumption;
• chemotherapy;
• tumors in the nasal cavity or the base of the skull.

The decrease in smell can have serious consequences on health and quality of life:

• loss of retro-olfaction during feeding, that is to say the ability to perceive the aromatic characteristics of food contained in the mouth;
• loss of taste;
• loss of the ability to detect certain hazards such as gas or smoke emanation;
• food poisoning due to the inability to recognize the smell of spoiled food;
• disturbances or loss of appetite;
• undernutrition, especially among the elderly;
• psychological and social difficulties;
• even depressive episode.

Odor tests can be performed by otolaryngologists or ENT doctors to assess the state of the patient’s olfactory functions. If a disorder is detected, more precise examinations such as a nasal fibroscopy, an X-ray or a CT scan may be done in addition to diagnose possible hyposmia. 

Hyposmia is reversible when its causes are curable. Thus, if it is due to a viral infection, the odor disturbances usually disappear at the same time as the other symptoms of the infection. In all cases where the loss is reversible, the smell recovery process can take from a few weeks to several months.

In some cases, the hyposmia can be irreversible. In particular, in the event of cranial trauma having caused deterioration of the olfactory nerves, treatment is difficult to achieve.

Depending on the cause identified, specific treatment may be offered:

• viral infection: symptomatic treatment or even treatment with inhaled cortisone to promote recovery of smell;
• nasal polyposis: treatment with cortisone, endo-nasal surgery being performed only after failure of several well-conducted medical treatments;
• allergies: avoidance of the allergen and treatment of symptoms.

Olfactory rehabilitation can also be offered to stimulate the sense of smell. It consists of smelling, several times a day, for a few minutes and over several months, various odors:

• from essential oils such as extracts of lemon, clove, rose, eucalyptus etc. ;
• everyday life in the kitchen, when you enter a perfume shop or a cheese factory, or even during a walk in the forest.

The more the patient receives olfactory stimuli, the more he increases and preserves his sensory acuity.