Published on 17. June 2021

Just follow the nose

We can rely on our olfactory organ, it plays a central role in our lives. The sense of smell is the most immediate of the human senses, without it we could not taste. It warns us, is closely linked to feelings and memories, and influences our social environment.

THE NOSE is the most underestimated sense organ. The olfactory epithelium at the back of the nasal sinus and the areas responsible for processing the stimuli in the brain distinguish more than a trillion odors! The tongue, on the other hand, recognizes just five tastes, the eyes up to 7.5 million color tones and the ears around 340,000 sound qualities.

Highly complex processes

A person inhales and exhales more than 20,000 times a day, each breath carrying millions of scent molecules into his or her nose. Everything that smells emits tiny scent particles, and the molecules are carried with the airflow through the nasal cavity to the olfactory cleft in the roof of the nose. There they dock onto the more than 20 million olfactory receptors located in our nasal mucosa. These tiny sensory sensors inform the brain about the scent. For this to happen, the scent and the receptor must fit together exactly, like a key in a lock. When one of the 350 different receptors is activated, it causes an electric current to flow to the brain - as a result, we can then interpret a spice, the sea or flowers, for example. Biological scents, for example, combine a mixture of several hundred scent molecules. The nose identifies this mixture, each of which activates a specific combination of the receptors present - precisely those for which the scent of this mixture was present.

Primitive people can do it better

The olfactory sensitivity of people from industrialized nations is weaker than that of primitive peoples. Causes can be environmental pollution, the overloading of our noses with synthetic odors, or even a lack of training. None of our senses stimulates our emotions more than smelling. If we stretch our nose into the world, a lot can happen: Freshly ground coffee reminds us of cozy get-togethers with the family, the smell of Christmas cookies makes us feel again the disappointment that the presents for the sister on Christmas Eve turned out to be bigger and bigger, the smell of gasoline fills us retrospectively with pride in the first car we owned.

While visual, acoustic or haptic signals must first be processed in the cerebral cortex of the brain, scents have a direct effect on the limbic system, where emotions are processed and drives are directed. Olfactory perception - the sense of smell - is located in the biologically oldest part of the brain. Especially in the early days of mankind, it fulfilled an important function: it warns of danger from fire or gases, helps in the search for water and food, decides between edible and inedible food. Even the fear sweat of other people can be smelled - a decisive advantage in battle or in the presence of danger.

Love smells good

When you enter a room for the first time or meet someone you don't know, your sense of smell usually gives you your first impression. The choice of a partner also depends on smell - something we are not aware of in most cases. If two people have the right "chemistry," this is to be understood quite literally and refers to the scent of the other person. This is because the scent molecules that a person secretes contain information about the nature of his or her genetic makeup.

Research on mice and other mammals has shown that these animals prefer partners whose genetic material differs as much as possible from their own. This ensures that potential offspring are equipped with particularly good genes, for example by making the immune system particularly resistant. Researchers have found that close relatives often "can't smell each other" in adulthood. The conclusion: incest, which usually leads to genetic defects in the children, is thus avoided. Dislikes, developed over time, also influence the sense of smell. Women, for example, report that they cannot stand the body odor or aftershave of their ex-partner or their irascible boss.

Babies rely on their nose

The sense of smell is already fully developed in newborns, allowing them to find their mother's breast. Olfactory memory develops primarily in the first three years of life, during which time babies collect the majority of their olfactory impressions - they all leave a trace in the brain. Expectant mothers, for example, are extremely sensitive to smells, especially in the first trimester of pregnancy; many show aversion and reluctance to certain foods, perfumes or smoke. Biologists explain this phenomenon as a protective mechanism to protect the unborn child from potentially harmful influences from food or the environment. In the first three months, the embryo is particularly sensitive; vital organs are formed during this time.

Olfactory perception weakens from the age of 40. The ability to recognize and distinguish scents diminishes. Smoking or intensive contact with chemicals, dirt, dust also contribute to this. Those who lose their sense of smell completely suffer from "anosmia". Reasons for this can be destroyed olfactory nerves, chronic inflammations, allergies, but also brain tumors or Alzheimer's disease. In connection with a COVID-19 disease, the perception of smell is impaired in at least one in two people, and the impairments usually disappear after a certain time. Permanent loss of the sense of smell can have serious consequences. Many of those affected suffer from psychological problems. For example, because they are no longer sure whether their own smell is too strong and possibly disturbs others. For example, they develop a compulsion to wash or withdraw completely from life.

The most common treatments for olfactory disorders include surgical therapy or the use of corticosteroids (hormones produced in the adrenal cortex). Conservative therapy involves the use of topical (e.g., applied) or systemic (e.g., tablet, infusion) corticosteroids. Depending on the indication, surgical options include endoscopic sinus surgery. Often, conservative therapy must be continued after surgical intervention.

Three questions for Tatiana Jähn, senior physician at the Department of Otolaryngology, Head and Neck Surgery, Plastic Surgery at Vivantes Klinikum im Friedrichshain.

Ms. Jähn, is the sense of smell similarly pronounced in all people?

No, about five percent of the population are anosmic - an extreme case of an olfactory disorder: they suffer from the absence or loss of the ability to smell. There are also people who are hypersensitive or diminished sensitive. They perceive odors altered in the presence of a stimulus source or smell something without a stimulus source being present.

What specific olfactory problems do your patients usually have?

Predominantly, they suffer from decreased sensitivity or complete loss of olfaction, usually caused by chronic rhinosinusitis (simultaneous inflammation of the nasal mucosa - rhinitis - and the mucosa of the paranasal sinuses - sinusitis), with or without polyps. Inflammatory or mechanical causes are responsible, for example, obstruction of access to the olfactory epithelium. Even obstructed nasal breathing due to a crooked nasal septum can disrupt the transport of olfactory substances. Furthermore, we ENT physicians also see patients after craniocerebral injuries on a consultative basis. Olfactory disorders after trauma are caused, for example, by a rupture of the nerve fibers or a brain contusion (brain contusion). Viral infections are also accompanied by olfactory dysfunction caused by damage to the olfactory epithelium. Olfactory dysfunction may also be an early symptom of a neurodegenerative disease (Alzheimer's, Parkinson's, Huntington's disease).

How can you help?

In the foreground of the treatment of nasal diseases that are causative for an olfactory disorder are, for example, surgical therapy or the use of corticosteroids (hormones that are produced in the adrenal cortex). Conservative therapy involves the use of topical (e.g., applied) or systemic (e.g., tablet, infusion) corticosteroids. Depending on the indication, surgical options include endoscopic sinus surgery. Often, conservative therapy must be continued after surgical intervention.

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