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Every day we actively interact with the outside world with the help of our senses – sight, hearing, smell and touch, taste. But anyone who has developed severe nasal congestion at least once in their life due to an infection or a severe allergy has experienced what it is like to be without one of our primary senses: our sense of smell.
In most animals, the sense of smell is absolutely essential for survival, reproduction, and rearing of young. Although people can survive without their sense of smell, studies have shown that its loss negatively impacts quality of life, even leading some people to become clinically depressed. Just as other animals depend on the sense of smell as a danger signaling system, we also depend on smell. A normal sense of smell will alert us to the danger of smoke in a fire, a natural gas leak in a house, and spoiled food.
On a daily basis, the smell complements our life experience and is often an integral part of our memory of the events of past years. Memories of the perfume your spouse wore or the bread baked at your grandmother’s house when you were a child last for decades and are often closely associated with strong emotions.
The taste of food is also largely dependent on the sense of smell, and without it, food is just a way to eliminate the feeling of hunger. Given our social activities associated with visiting restaurants, bars and cafes, it is understandable how a person who has lost his sense of smell can develop a sense of alienation.
Olfactory disorders affect 19% of the population over 20 and 25% of the population over 53. If we consider the loss of smell only as a result of aging, then one in eight people between the ages of 53 and 91 notes a gradual decrease in their sense of smell. The detrimental effect of loss of smell on the taste of food can significantly affect the elderly population, and diet and proper nutrition are becoming irrelevant.
Causes of loss of smell
The sense of smell depends on millions of specialized nerve cells that are located in a deeply protected recess high in the nasal cavity. Remarkably, these nerve cells usually die and are replaced throughout our lives. Therefore, the system is able to repair itself after an injury, but this is not always possible.
Loss of smell is caused by several different factors. Some babies are born without a sense of smell. This is due to an underdeveloped chemical sensory system. The chemical sensory system does not release molecules that send signals to the specific part of the brain where odors are detected. The center of smell is a complex little nervous system located in a patch of tissue at the very top of the nose. This nervous system is directly connected to the brain. If a section of nerves is underdeveloped or damaged, a person may lose their sense of smell.
Causes of anosmia (loss of smell) in humans:
- head trauma;
- severe injuries to the upper part of the nose;
- severe upper respiratory tract infections;
- polyps in the sinuses or nasal passages;
- tobacco smoke;
- inhaling certain chemicals, such as pesticides or ammonia, for a long time (many years);
- hormonal imbalance;
- some dental problems;
- certain prescription drugs you take;
- radiation therapy (if performed on the neck or head);
- colds and allergies;
- some diseases of the central nervous system (Alzheimer’s disease).
- tumor of the anterior cranial fossa.
In some cases, the loss of smell is complete (anosmia), while in other cases there is only a partial loss (hyposmia). In many cases, when there is a partial loss of smell, the remaining odors are distorted. Distortions are either felt as smells that smell sharply different from what is remembered (parosmia), or as a smell that is not there (phantosmia).
Perhaps if they were pleasant, then these distortions of smell might not be so painful. However, in almost all cases the distorted odors are unpleasant: patients describe them as smoky, swampy, musty, trashy, or chemical. It is usually difficult for people to describe the smell as it is unlike anything they have experienced before.
Treatment for loss of smell
Loss of smell is called anosmia. For most people, the loss of smell begins to worsen after the age of 60, and most older people lose their sense of smell almost completely. Experts believe that the ability to smell is at its peak between the ages of 30 and 60. In addition, women have a better sense of smell than men.
Anosmia and taste are related. Many people who lose their sense of smell, or those born without a sense of smell, also lose their ability to taste. Scientists believe that this is due to the fact that people “taste” food by smell, texture and temperature. In addition, many people can recognize their food or drink by smell. Coffee is a drink that is liked not only by its taste, but also by its smell.
If you have symptoms and signs that accompany your anosmia, you should see a doctor. Symptoms to be concerned about include:
- lack of smell and taste of food;
- stuffy nose and impaired nasal breathing;
- persistent sneezing, nasal discharge, and itchy eyes;
- weight loss;
- headache;
- nose bleed.
Diagnostics
The diagnosis of anosmia is made by carefully examining symptoms and considering any past events that may have caused anosmia, such as a recent head injury or nasal congestion from an upper respiratory infection. The nasal passages are examined and a test kit is used, which includes materials with an intense odor. It helps to determine if severe odor loss has occurred. If the cause of anosmia is not obvious, a CT scan or MRI of the head may help identify neurological causes.
Modern treatments
Under certain conditions, such as colds, severe upper respiratory infections, and allergies, you should restore your sense of smell after the illness clears up. If an allergy is the cause of the problem, the doctor uses medication to relieve allergy symptoms (Cetrin, Zirtek, Claritin, Suprastinex, Kestin) to treat it. Several antiallergic drugs are used to successfully treat anosmia. If polyps are the cause of anosmia, surgical removal is an option to restore your sense of smell. Sometimes a person who has lost their sense of smell can regain it without any treatment.
Popular questions and answers
We asked neurologist of the highest category Galina Chudinskaya about the loss of smell and possible problems associated with it.
– The olfactory receptors located in the upper nasal passage are surrounded by supporting cells, without which the olfactory cells cannot function. These supporting cells can produce the ACE2 protein that the coronavirus uses to enter the cell. Olfactory cells do not have ACE2, which means they are not infected by the coronavirus.
Thus, there is an assumption that it is these supporting cells, without which the olfactory receptors cannot function, that become infected and die.
When the virus enters the supporting cell thanks to the ACE2 protein and causes swelling, the olfactory neurons remain intact, but are covered by swollen surrounding tissues and aroma molecules cannot reach them.
When the healing process begins and the immune system copes with the virus, the swelling subsides, the aroma molecules have free access to intact receptors, and the sense of smell returns to normal.
If the inflammation is extensive, it can also damage neighboring cells – olfactory neurons. This is the second stage. Olfactory neurons regenerate from stem cells in the nasal mucosa, but this takes a longer time and the sense of smell recovers much more slowly.
Deeper lesions also occur. There is an assumption that in some cases the virus can affect the entire olfactory tract: both the olfactory nerve and the olfactory bulb, which contains intermediate olfactory neurons, and the part of the brain that is responsible for the perception of odors. Therefore, the question of how deeply a virus can penetrate our central nervous system and damage it remains open and is being studied.
Is the loss of smell always a sign of illness?
When the sense of smell is suddenly lost, the likely cause is an infection, a side effect of medication, a head injury, or exposure to a toxin. When the sense of smell gradually disappears over time, the more likely cause is sinus inflammation, chronic obstruction from an infection or allergy, or a progressive disease such as Alzheimer’s. Slow onset and progression of loss of smell can also be a normal part of aging.
– Loss of smell can occur, for example, with the flu and other viral infections, – says neurologist Galina Chudinskaya. – It can occur with damage to the central nervous system, for example, trauma or swelling of the anterior cranial fossa, in which the olfactory nerve passes.
How long can the loss of smell last?
– If the sense of smell is not restored within 2 months or more, then one should turn to medical treatment, which is usually used for lesions of the central nervous system, advises neurologist Galina Chudinskaya. – This is the stimulation of acetylcholine transmission with the help of drugs and translingual neurostimulation, which is used in other focal lesions of the central nervous system and peripheral nervous system, stimulating the transmission of impulses and accelerating the process of regeneration of the sense of smell.