Intuitively, we seem to smell our nose. In fact, many systems are involved in this process. First, a molecule of a substance (for example, pollen) must stimulate special nerve cells located high in the nose. Then these cells send information to the brain – and that’s where it gets overgrown with nuances of meaning, saturated with emotional content.
A “short circuit” at any node of this system can lead to the fact that odors either disappear altogether, or become subtle, or even begin to arise out of nowhere, without an obvious source. All of this is unpleasant in itself, but it can also be a sign of a serious illness.
Nasal congestion
The oral and nasal cavities are the first to fight infection. Their surfaces are lined with mucous membrane, the cells of which, if necessary, can produce mucin (mucus) – a liquid that has disinfecting properties. When the nose “flows”, it is mucin that flushes out the infection.
Mucus also serves as a medium for transmitting information from odorants, molecules that carry odors. But if the infection becomes too much, there is swelling of the mucous membrane, which blocks the olfactory receptors in the tissues of the nose. This can happen with viral diseases and allergies.
With chronic sinus infections or severe allergies, the loss of smell can be permanent. In this case, sensitive cells may even die off, and then even with relief of symptoms, the sense of smell will remain reduced.
Viral infections
The virus can directly attack the cells in the body that provide sensitivity to odors. It is this ability that SARS-CoV-2 possesses, because of which we suffer so much today. is he penetrates into cells by clinging to the ACE2 receptor in goblet cells, which line the mucous membrane of many organs, including the nose.
In this case, the loss of smell is not accompanied by abundant mucus production, but, on the contrary, by dryness, itching and other unusual sensations. Some coronavirus patients have not only a loss or dullness of their sense of smell, but also phantom odors: for example, when strawberries suddenly begin to give off burnt rubber.
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Smoking
On the mucous affects approximately 4720 toxic substances from tobacco smoke. Regularly getting on the cells of the olfactory and gustatory systems, they inhibit their functions, and with long-term exposure, they change their structure. The degree of injury depends on the properties of the plant and the duration of exposure.
The substances in smoke can act in different ways: kill mucus-producing cells (which causes dryness in addition to loss of odors) or provoke their overgrowth, which leads to increased mucus production and “perpetual runny nose”.
Generally reduced sense of smell in smokers meets almost six times more often than non-smokers.
Neurodegenerative diseases
Smell disorders can occur in the early stages of disorders associated with depression of the nervous system, such as multiple sclerosis, Parkinson’s and Alzheimer’s disease. This often happens long before other symptoms appear, and the person may not attach any importance to this and not see a doctor.
For example, only 3.3% of patients with some form of parkinsonism do not experience problems with smelling. For the majority, it decreases or disappears altogether. At the first signs of Alzheimer’s disease, the general ability to detect odors gets lost, and in the later stages, a person ceases to distinguish them. In multiple sclerosis, a decrease in sense of smell occurs in about a third of people and progresses over time.
The specific reasons are different in all cases, but most often they are associated with damage to the brain substance or the pathways through which the signal enters it. For example, in the case of Algzeimer’s disease, it may also be the primary olfactory cortex, where odors are processed; and the hippocampus, which links them to memories; and the hypothalamus, which regulates the emotional side of odors.
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Brain injuries and tumors
Any damage that affects the olfactory structures (tumors, parasitic infections of the brain) can affect the perception of smell. For example, in one study, reducing sensitivity to odors noted in about half of patients with concussion.
The same logic applies here as in neurodegenerative diseases: if structures that are supposed to process information from nasal receptors are hit, this information will be distorted. Fortunately, with successful removal of tumors and recovery from injuries, the sense of smell returns to normal.
Mental disorders
Here the connection is even more interesting. In order for us to fully experience the smell, many structures with different functions must be involved. The zones responsible for emotions and the perception of smells overlap each other, so the oppression of any of them can deprive the world of the fullness of aromas we are used to. For example, people with severe depression may arise disturbances in structures associated with emotions. Then pleasant smells will be felt muffled, and unpleasant – on the contrary, stronger.
With bipolar disorder (when the stages of mania and depression replace each other), a person may be haunted by unusual smells that appear as if from nowhere, for example, the smells of rotting flesh, dirt. In schizophrenia, odors can be either dull or, conversely, very strong. Disruptions of this kind can accompany alcoholic or drug psychosis.
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Taking medication
Loss of smell is a side effect that celebrated more than 250 drugs. Some medications, especially antihypertensive drugs and antihistamines, can sometimes have this effect. This is mainly due to the vasoconstrictor properties, which can reduce swelling. The tissues of the nose are not sufficiently saturated with blood, and their sensitivity decreases.
Some drugs are of particular concern to doctors. For example, there has been a controversy in the US medical community for years about zinc sprays. FDA regulatory agency two years ago called on stop using zinc-containing preparations due to dozens of reports of loss of smell, including constant loss.
Toxic substances
Exposure to harsh chemicals such as insecticides or solvents can burn the sinuses and permanently damage receptors. Common culprits are methacrylate vapors, ammonia, benzene, cadmium dust, chromate, formaldehyde, hydrogen sulfide, nickel dust, and sulfuric acid. Therefore, to protect yourself, it is better to work with strong-smelling chemicals in a respirator mask. Disposable sheet masks do not provide adequate protection.
Age
Our ability to perceive odors decreases throughout life. As a rule, we do not notice this, because the decline is gradually… Only olfactory tests can determine this exactly. A dull sense of smell occurs in more than half of people between the ages of 65 and 80 and in three quarters of people over the age of 80. Most often this is due to the consequences of chronic diseases, decreased immunity and age-related brain damage.
In any case, an unreasonable loss of smell (or the appearance of bizarre odors) is a good reason to see a doctor. Especially if it’s not the only episode.
Anton Soldatov
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