The physician and biologist Hanns Hatt, professor at the Ruhr University Bochum, has been on the trail of the riddle of smell for decades. He decoded the first human olfactory receptor and later proved that such receptors are not only found in the nose, but also in other tissues, such as the heart, the intestines or in tumor cells. Hatt even found olfactory receptors in skin cells, the activation of which accelerates wound healing, for example. “But to date,” says Hatt, “scientists have not been able to determine a person’s own odor.”
The body odor is unique
But one thing is clear: Every human owns one individual scentwhich is produced by a special species of sweat glands— the apocrine Drüsen – is formed and secreted as a secretion. These glands are mainly found on hairy parts of the body: on the scalp, in the genital area and under the armpits. The hairs work like wicks, transporting the secretion away from the skin and into the air. As such, they play an important role in mysterious communication between skin and nose.
What the skin has to communicate is far more than what we consciously perceive as an odour. “Science is still arguing about whether the secretion of the scent glands is responsible for the odor itself or whether it is created by the bacterial decomposition of the secretion on the skin’s surface,” says Hanns Hatt. The latter thesis would at least explain why every human being has an odor mixture that is only characteristic of him. The surface of the skin is populated with a bacterial population whose composition is also determined by the individual immune system. This microbiome transforms the glandular secretion into a kind of olfactory signature.
Vegetarians smell better than meat eaters
This stable part of the inherent odor is joined by more variable parts such as sweat and other exhalations influenced by metabolism. The consumption of garlic or onions, for example, is quickly communicated through the skin. The diet itself also has an influence on a person’s scent signet. The smell of vegetarians is described as more pleasant than that of meat eaters.
In addition, there are the pheromones, olfactory perceptible odor messengers of the skin, which are identical in all members of a species and, at least in the animal kingdom, trigger the same reaction in all. While dogs have a multitude of pheromone receptors in a specific region of the nose – called the Jacobson’s or vomeronasal organ – this organ is no longer functional in humans. Only in the olfactory mucosa five types of pheromone receptors have been discovered today. “Apparently we don’t communicate much about these messenger scents anymore,” states Hatt.
Body odor reveals emotions
Neuropsychologist Ilona Croy, who researches olfactory communication at the University of Jena, therefore prefers to speak of “socially relevant smells” because they do not trigger a standardized reaction in people: “We have too much cognitive superstructure for that.” However, people react to such socially relevant smells are at least “different,” according to Croy. At the University of Düsseldorf, the psychologist Bettina M. Pause is researching the topic of “smell and emotion”. In one experiment, she had students wear cotton pads under their armpits before an exam.
Smelling the “fear cotton” triggered a reaction pattern of fear, attention, concentration and empathy in other people. “Chemical fear signals are able to transfer feelings from one person to another,” states Pause in the non-fiction book “Everything Smell Matter”. In other words, fear is contagious. And the infection occurs – also – via the nose. It is still unclear exactly how this works.
“Humans cannot unequivocally assign smell samples to a specific emotion or character trait,” Croy says. The inherent smell would rather leave a “holistic overall impression”: if we smell another person, we cannot say that they are dominant, somewhat stressed and vegetarian, for example. But we can divide smells into likeable and less likeable. Those scent samples where the donor is healthy and not stressed or anxious are disproportionately often referred to as “likeable”.
Body odor can indicate certain diseases
But body odor also conveys other messages. “In almost all diseases that we know of, the odor spectrum of the affected cells in the tissue changes,” explains cell physiologist Hatt. Sometimes this can also be felt through the skin. Ammonia-smelling sweat can indicate a kidney problem, an essign note in body odor in a hypothyroidism be justified. Specially trained dogs sniff out impending hypoglycaemia in diabetics and an impending seizure in epileptics. Dogs are also used successfully in cancer diagnostics as detectors for lung, breast, bladder and breast cancer prostate cancer deployed.
How smell signals control mating behavior
Scent samples from Women in the fertile phase are perceived positively by men. Vice versa can women men smell good: For a study at Birmingham University, a chair in a waiting room was sprayed with the male hormone androstenone – with the result that significantly more women sat there than men. Sexual orientation also plays a role. Psychologist Pause concludes from initial studies that homosexuals react differently to the smell of women and men than heterosexuals.
Body odor also conveys information about the other person’s immune system. To be more precise, by equipping it with MHC molecules (Major Histocompatibility Complex), with the help of which the body recognizes and destroys foreign cells. Each person has a specific MHC system, only identical twins have identical defense systems. Several studies indicate that women (here the research situation is better than that of men) find the scent of men more attractive whose MHCG pattern is rather different from theirs.
This makes sense from an evolutionary point of view: the combination of two different immune systems is better protected against viruses and bacteria. According to neuropsychologist Croy, however, this has a rather subordinate effect on modern pair formation. In the complicated life of people willing to commit, there are stronger influencing factors today than smell – also because Tinder & Co. only present potential partners visually and not olfactorily.
Body odors bring families together
However, olfactory perception offers at least a certain protection against incest. Because the “stable smell” brings families together: People can tell quite well from the smell whether a shirt was worn by a relative or a stranger.
This one seems the strongest connection between mothers and their children. Just a few hours after birth, infants prefer the smell of their mother to that of a strange woman. Conversely, in mothers, the smell of their baby activates the reward center in the brain and can thus strengthen the mother-child bond. Croy speaks of a kind of baby smell “olfactory child scheme”: Even if it is not yet clear what defines it chemically, everyone likes baby scents. A clever mechanism of evolution. Because that’s how the father and other adults like to take care of the baby.