Why is body odor considered so offensive?

The olfactory system in humans. The influence of smells on behavior

Table of Contents

1. The importance of smell
1.1. The smell in different historical epochs
1.1.1. The beginnings of perfume culture
1.1.2. The sense of smell in ancient and medieval Greece
1.1.3. The rediscovery of the sense of smell in the Renaissance
1.1.4. The smell in the Rococo and during the Enlightenment
1.1.5. The smell in the 19th century
1.1.6. The transition into the 20th century
1.2. The importance of the sense of smell
1.2.1. The Neanderthal man
1.2.2. The sense of smell today

2. The olfactory system (sense of smell)
2.1. Man's nose
2.2. The structure of the olfactory system
2.2.1. The nasal cavity
2.2.2. The olfactory mucosa
2.2.2.1. The structure of the olfactory mucosa
2.2.3. The odorant binding proteins
2.3. The olfactory bulb
2.4. The olfactory brain
2.5. The limbic system
2.6. The signal transduction of the olfactory receptor cells
2.7. The vomeronasal organ
2.8. The nasal-trigeminal system
2.9. The loss of the sense of smell
2.10. The localization of the olfactory complex

3. The influence of smells on behavior
3.1. The smell imprinting in the womb and in newborns
3.2. The sense of smell in children and adults
3.3. Changes in the sense of smell with age

4. General influences of the sense of smell on sensation and behavior
4.1. Feelings of trust and security
4.2. Attention and risk taking

5. Pheromones and their effects on human behavior
5.1. What are pheromones?
5.1.1. The different types of pheromones
5.1.2. The pheromones in the wildlife
5.2. The role of sex attractants in partner choice

6. Summary

7. Bibliography

8. List of images

9. Affidavit

1. The importance of smell

The sense of smell, like the gustatory sense, is one of the chemical senses. The receptors in the nose convert chemical information into electrical signals. These signals reach the cerebral cortex via the olfactory bulb, where they are converted into known or as yet unknown odor sensations. This is how man smells.

In the course of evolution, however, the sense of smell has lost much of its importance. In its original form it is a remote sense. Through it one is informed over great distances, it signals food sources as well as danger. You can't see escaping gas, but you can smell it. Just as you smell a fire long before you see it. In addition, the sense of smell plays an essential role in controlling food and in initiating the digestive reflexes. An apple that looks nice but smells musty is not eaten.

Often, however, the sense of smell is described as a ’lower’ sense, since at first glance people would rather do without it than the sense of sight or hearing. Smells are better memorized than other sensory impressions. It's harder to remember a face in old age than a childhood smell. One of the reasons for this is that the smell is the sense that you cannot turn off. You can cover your ears, close your eyes or don't touch anything for a while, but with every breath you smell and so constantly absorb odors. The smell awakens memories and longings for the past through associations, it determines and influences people's feelings and actions.

1.1. The smell in different historical epochs

In every era, smell has played a special role, be it in the early days, in which prehistoric man also found his prey by smelling, or in modern times, in which the natural scent of man is perceived as unpleasant and covered with perfume .

1.1.1. The beginnings of perfume culture

The oldest culture in the world, that of the Sumerians, was already known for more than 3000 BC. An early form of perfume production. They extracted essential oils from plants and used them to produce perfumed anointing oils, among other things. They also cultivated the custom of grave goods. So they placed their queen Schub-ad (around 3500 BC) in addition to jewelry and a golden make-up box in her grave [Ohloff, 2004].

Also in ancient Egyptian graves (around 3200 BC) there were ointment and perfume vessels as well as make-up palettes. In the grave of Tutankhamun, hermetically sealed nard oil was found, which was one of the most precious perfumes in ancient times. The Queen of Sheba allegedly brought it to King Solomon as a gift and even Jesus is said to have been anointed with this oil by Mary Magdalene [John 12, Verse 3].

1.1.2. The sense of smell in ancient Greece and in the Middle Ages

In ancient Greece, smelling and touching were often viewed as vulgar, often even dirty, activities, while hearing and, above all, seeing were viewed as ’noble’ actions. Although Aristotle (384 - 324 BC) established a connection between fragrances and the human soul [“Man cannot smell what is smell without feeling unpleasant or pleasurable”; Ohloff, 2004], both Socrates and Plato opposed the use of fragrances. Plato spoke of the "softening of men" [Vroon, van Amerongen, de Vries, 1996], he was even of the opinion that perfume should only be reserved for prostitutes.

Over time, however, opinion changed, and more and more people adopted Aristotle's views. They were convinced that their souls would have a scent, since fragrances should be attractive to the gods.

Unlike in late antiquity, however, the importance of the sense of smell was consistently viewed negatively in the Christian Middle Ages. He was considered offensive and a trigger of lust (one of the seven deadly sins).

1.1.3. The rediscovery of the sense of smell in the Renaissance

It was not until the Renaissance that greater importance was attached to the sense of smell. The English Queen Elizabeth I wore a small linen bag around her neck containing a mixture of fat extracts made from cinnamon, cloves and rotten apples. According to Goethe, Friedrich Schiller is also said to have found the smell of rotting apples stimulating. It is said that Schiller always hid a few apples in the drawers of his desk because their scent made it easier for him to concentrate on his work. [Ohloff, 2004]

1.1.4. The smell in the Rococo and during the Enlightenment

In the Rococo period, the French court was the leader in terms of the predominant fragrances. Under Louis XIV, who was also known as ’roi très parfumé’, strong floral fragrances were in demand, which also served to cover up the usually strong body odor. Marie Antoinette, the wife of Louis XVI, rejected these harsh fragrances, which often contained animal secretions. She preferred fresh scents based on rose water and lemon aroma. Especially the ’Eau de Portugal’, which was widespread at the time, was one of her favorites.

During the Enlightenment, however, the sense of smell was again viewed disparagingly. Kant, one of the leading enlighteners, was of the opinion that "the smell is considered to be 'lower sense' and should therefore be viewed as primitive. There is no reward in cultivating it ... ”[Ohloff, 2004] Many scholars shared Kant's attitude and joined his categorical imperative. For them, "the sense of smell was the’ most ungrateful ’and also’ most dispensable ’, ... that can be found in the animal kingdom." [Ohloff, 2004]

1.1.5. The smell in the 19th century

In the 19th century, the ancient idea of ​​the fragrance of love as a theme returned to literature. Baudelaire writes about the scents of incense in churches, about musk and the scent of youth, Emile Zola about the deafening scents of women and men. The protagonist of the novel “Nana”, Count Muffat, “soaks in the entire sex of women in one breath.” [Ohloff, 2004]

The smell also plays a role in a large number of proverbs, for example there is the “scent of youth” and the “scent of the past”. The linguistic field is large for designations of the human nose, so a successful person with a keen sense has a “good nose” or a “fine nose”. But the smell has also found its way into everyday language. “You can't smell someone”, “something stinks” and “something is drowned and lies” are just a few examples of the linguistic reliance of the German language on the term “smell”.

During this time Eugene Rimmel presented the world's first perfume fountain at the London World's Fair in 1851. Tiny fragrance molecules were released into the air by steam distillation. Many department stores still use this idea today by using their ventilation systems to convey fragrances into the rooms in order to raise the mood of customers and stimulate their desire to buy [Ohloff, 2004].

1.1.6. The transition into the 20th century

Charles Darwin, made famous by "The Origin of Species", took the view that "smell is the lost sense that has receded in the course of development" [Ohloff, 2004]. Towards the end of the 19th century, Siegmund Freud formulated the thesis that the sense of smell was only of subordinate importance and thus supported Kant's conviction. At the beginning of the 20th century, the dreams and emotions triggered by smells were taboo and viewed as indecent. In addition, there were still controversial opinions about personal hygiene and hygiene measures. Quite a few people were of the opinion that a layer of dirt on the skin prevented the deposition of bacteria. In addition, “the organism softens if it comes into contact with water too often.” [Vroon, van Amerongen, de Vries, 1996] This opinion was particularly contradicted by the medical profession, and they set out new bathing regulations. The body should be washed thoroughly two to three times a week, as clean skin would rid it of pathogenic bacteria.

The physician Semmelweis, also known as the ’savior of the mothers’, examined mothers who had died of puerperal fever as early as 1847 and found that the death rate could be significantly reduced by washing hands by doctors and midwives as well as other disinfection measures between the individual examinations. In his clinic, the death rate fell by a good 90%, but his findings did not prevail, on the contrary, Semmelweis was committed to an institution for mental disorders due to an intrigue, in which he also died. It was only decades later that his theses found general recognition. [Vroon, van Amerongen, de Vries, 1996]

1.2. The importance of the sense of smell

The sense of smell not only serves to search for and take in food, it also has a protective function. If you perceive a harmful smell, hold your breath so as not to inhale it and leave the room. It also provides orientation in the environment and influences people's social behavior. It is not uncommon to use the expression “you cannot smell someone” to express a certain antipathy. However, group formation or partner choice behavior also seem to be positively influenced by smells in humans.

In the course of evolution, however, the importance of the sense of smell has changed as well as the physiological requirements of humans.

1.2.1. The Neanderthal man

The skull of the Neanderthals was elongated and narrow, the flat receding forehead ended in a strongly pronounced bulge above the eye (Supraorbital torus). This bone thickening is still found in great apes today, but in humans it has long since disappeared. Compared to the mouth and nose region of today's humans, that of the Neanderthals was clearly protruding, the receding chin serves as a good distinguishing feature from modern humans. The cheekbones also fell back slightly. Her jaw was strong and adapted to the food available at the time. In their shape and number, the teeth of the Neanderthal man correspond to those of modern humans, but the incisors are enlarged. The so-called "Neanderthal gap" is also concise, it occurs between the last molar (Molars) and the branch of the lower jaw. A crest (Crista sagittalis), unlike in great apes and earlier human forms, no longer occurs.

The "teeth-as-tool" hypothesis assumes that the teeth of the Neanderthal man served as a tool in addition to eating. They were used as a kind of vice and pliers. The typical shape of the skull is said to have resulted from this heavy load [Landeshauptstadt Hannover, Schulamt, 2001].

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Fig. 1.1: Reconstruction of a Neanderthal skull [www.ndrtv.de]

The Neanderthals were dependent on their good sense of smell, through which they were warned in life-threatening situations. In contrast to today's humans, their nostrils were wider and more powerful. Researchers suspect that the Neanderthals had large and fleshy noses, an adaptation to the Ice Age [Czarnetzki, 1998]. Her broad nose warmed the air she breathed in before it reached her lungs. In this way, the Neanderthals were able to maintain their body temperature better in cold climates. In addition, recent research suggests that their olfactory mucosa seems to have been arranged further forward than it is today Homo sapiens sapiens. That way they could smell better and have an advantage when hunting. In contradiction to this, however, is the fact that today's humans in areas far from the equator have a rather narrow and high nose, which is exactly the opposite of the Neanderthals. The researchers are still unclear how this can be explained [Czarnetzki, 1998].

Figure not included in this extract Fig. 1.2: Homo sapiens neanderthalensis [www.de.wikipedia.org]

1.2.2. The sense of smell today

In the course of evolution, the pronounced sense of smell of the primate precursors was pushed into the background in favor of other senses. The Leipzig professor Svante Pääbo [Gilad, Man, Pääbo, Lancet, 2003] found in the analysis of human DNA (deoxyribonucleic acid, genetic information molecules) that about 60% of the olfactory receptor genes that were originally presumed to be present have become non-functional (pseudogenes) , because they are no longer read and transcribed into messenger ribonucleic acid (mRNA) (in great apes approx. 30% of the originally present genes for olfactory receptors are inactive). Pääbo and his colleague Yoav Gilad are of the opinion that the sense of smell had to give way to an improved sense of sight, since better color perception could have served to change the search for food [Gilad, Bustamante, Lancet, Pääbo, 2003].

Although humans are therefore not among the best users of the olfactory sense compared to many animals (microsomat), today's humans reflect more on the olfactory world around them, as research into the olfactory sense has also made great progress (Nobel Prize in Medicine 2004 to Richard Alex and Linda Buck for describing more than a thousand genes for olfactory receptors in the nasal mucosa) and just knowing its diversity sheds new light on possible meanings. A person with a "trained" nose can actually distinguish up to 1,000 different smell qualities. However, he usually lacks the words to sharply delimit the odor classes from one another. The 7 odor classes proposed by Amoore in 1952 (flowery, ethereal, musky, camphor-like, sweaty, putrid and pungent) still serve as guidelines today [Schmidt, Lang, Thews, 2005].

Like no other sense, smell has an emotional meaning, it determines and changes people's emotional world. The evaluation of fragrances is never neutral either, fragrances are always perceived as pleasant or unpleasant. They are linked to certain memories and thus trigger a multitude of sensations.

In the following, the influence of smells on human behavior will be examined in more detail. In addition, an overview of the role of pheromones should be given. First of all, however, the structure and function of the human olfactory system must be explained.

2. The olfactory system

People breathe in and out through their mouth or nose. However, he only perceives smells through his nose. The human olfactory organ lies in the center of the face. It has a different shape for every person, it can be long and narrow, wide, large, short and round (snub-nosed) or hook-shaped. The internal structure, however, is the same for all people.

2.1. Man's nose

From an anatomical point of view, the nose is one of the upper respiratory tract.It can be divided into two parts, on the one hand the outer, visible part, which is also known as the nasal framework, and on the other hand the inner part, which consists of the nasal cavities. In the outer nose, the immobile nasal bone in the upper part forms the basic structure. The cartilaginous part of the bridge of the nose connects to it in front and below. It is formed from the upper edge of the nasal septum and a so-called triangular cartilage to the right and left of it. The inner support structure of the nostrils, tips and openings is made up of the alar cartilages. The muscles and the skin lie on this outer part as protection from the outside [Schiebler, Schmidt, Zilles, 1999].

Figure not included in this excerpt

Fig. 2.1: Structure of the nose [www.dpsg-paderborn.de]

Via the nostrils (Nares), limited from the outside by the nostrils, the breath is taken in and into the nasal cavity (Cavum nasi) transported. From there it reaches the pharynx (Pharynx) into the windpipe (Trachea). The trachea branches into the two branches of the bronchi. The air is transported through the small bronchioles to the alveoli (Alveoli) promoted. Oxygen enters the capillaries through the thin walls of the membranes, while carbon dioxide is released from the blood into the lungs. This is how humans breathe [Schiebler, Schmidt, Zilles, 1999].

2.2. The structure of the olfactory system

The lining of the nasal cavity is covered with nasal hairs (Vibrissae) and cilia (Cilia) that filter tiny particles out of the air. In addition, it is lined with a mucous membrane that serves to enlarge the surface. The air is better humidified, preheated and cleaned with the help of cilia and mucus-producing cells.

The nasal septum (Nasal septum) separates the nasal cavity into two areas. Like the outer nose, it consists partly of bone and partly of cartilage tissue. The nasal septum acts as a support and thus ensures the shape and direction of the outer nose [Schiebler, Schmidt, Zilles, 1999].

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Fig. 2.2: Concha nasalis [www.de.wikipedia.org]

2.2.1. The nasal cavity

In the nasal cavity there are three superimposed protuberances on the side wall, the so-called turbinates (Conchae nasales). They serve to increase the surface area and also divide the nasal cavity into three nasal passages. The upper nasal passage (Superior nasal meatus) lies between the roof of the nose and the upper turbinate. In the back of this blindly ending corridor is the olfactory organ (Organum olfactus), which is why this duct is often referred to as the olfactory duct. The middle nasal passage, which also ends blindly, lies between the upper and lower turbinates (Meatus nasi medius). Another name for it is sinus duct because the sinuses (Paranasal sinus) are connected to it. The lower nasal passage, also known as the airway (Inferior nasal meatus) leads through the rear opening of the nasal cavity (choana opening) into the nasopharynx. Most of the air you breathe flows through this lower part of the nasal cavity. Presumably, therefore, less than 10% of the inhaled fragrances reach the actual odor center during normal breathing. This proportion can be increased through rapid breathing (“sniffing”) [Deetjen, Speckmann, Hescheler, 2005].

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Fig. 2.3: Cross section of the nasal cavity [Deetjen, Speckmann, Hescheler, 2005]

2.2.2. The olfactory mucosa

The nasal mucosa is divided into two different areas, on the one hand the respiratory mucosa (Respiratory region) and on the other hand into the olfactory mucous membrane (Regio olfactoria). The respiratory mucosa covers the two lower conchae. Here the breathing air is heated, humidified and cleaned. In contrast, the olfactory mucous membrane, which contains the sensory cells of the olfactory sense, only covers the upper concha, the nasal dome and on the upper parts of the nasal septum.

In humans it takes Regio olfactoria only a very small part of the total mucous membrane. It is only about 5 cm² in size and contains between 10 - 30 million olfactory cells. A dachshund, on the other hand, has around 120 million olfactory cells on a 75 cm² olfactory mucous membrane. In general, dogs are considered good macrosomats, while humans are microsomats [Deetjen, Speckmann, Hescheler, 2005].

2.2.2.1. The structure of the olfactory mucosa

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Fig. 2.4: Schematic structure of the olfactory mucosa [Schmidt, 1995]

The olfactory mucosa is a multilayered epithelium. It is made up of three different cell types, the basal cells, the supporting cells and the actual olfactory cells. The basal cells divide throughout their life; they develop into mature olfactory cells with an average lifespan of only one to three months. Due to their location, they are constantly exposed to toxic and infectious agents. For this reason, they need to be renewed regularly. The supporting cells hold the olfactory cells in their position. These have a bipolar structure and are among the primary sensory cells, i.e. they have their own axon and independently develop action potentials. A single dendrite forms at the apical end of the cell and runs through the entire epithelium.

This dendrite forms a thickened olfactory head on the surface of the mucous membrane, from which small cilia protrude. They are very thin, only approx. 30 - 60 μm long and form a dense, with olfactory mucus (Mucus) covered layer on the surface. The mucus is produced and secreted by Bowman's glands. It contains proteins that bind fragrances (odorant binding proteins), which presumably facilitate the transport of these fragrances to the olfactory cilia. The thin axon is located at the basal end of the olfactory cell. These axons bundle into several (Fila olfactoria) together and run through the ethmoid plate as the olfactory nerve (Olfactory nerve) directly to the olfactory bulb (Olfactory bulb).

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