I propose a challenge: would you be able to guess the age range of someone sitting next to you who is not wearing perfume using only your sense of smell? I have not found any challenge of this type on TikTok, but there is research that proves it: We can discriminate the age of a person by their smell.
Body aroma evolves throughout our lives, and the changes that occur not only have a biological explanation, but have also played an important role in social and evolutionary selection.
The smell of a baby strengthens parental affection
During childhood, body odor is usually mild due to low sweat gland activity and a simple skin microbiome (community of microorganisms). Even so, parents are able to identify the ‘fragrance’ that their own child gives off and prefer it to that of unknown children.
The odors that in this case generate a pleasant or familiar emotional olfactory perception (hedonic information) activate the neural networks of reward and pleasure and decrease responses to stress. Consistent with this, mothers with postpartum attachment disorders do not develop this recognition or olfactory preference for their own baby.
From a purely pragmatic evolutionary point of view, pleasurable identification of offspring would allow selective investment of resources.
Teenage scent of ‘humanity’
Adolescence involves a significant change in body odor. This transformation is due to the production of sex hormones, which, among other things, induces the activation of sweat and sebaceous glands.
While most sweat glands (eccrine glands) excrete water and salts, the so-called apocrine sweat glands (associated with hair and located in the armpits and genital area) secrete proteins and lipids. It is the joint degradation of these lipids and sebum (triglycerides, wax esters, squalene and free fatty acids) released by the sebaceous glands present throughout almost all of the skin that generates the characteristic aroma of ‘humanity’.
The decomposition of these substances occurs when they come into contact with the air and bacteria on the skin. Microorganisms such as Staphylococcus convert fats into acetic acid and 3-methylbutonoic acid, responsible for sour smell of teenagers.
Other volatile molecules that appear in greater quantities in the sweat of adolescents compared to that of children are androstenone (sweaty and urinary odor, similar to musk), androstenol (similar to sandalwood or musk) and squalene (rancid, greasy). or slightly metallic when oxidized).
The ability to recognize children by body odor decreases in both mothers and fathers when their offspring leave childhood and are in full adolescence. In fact, mothers even prefer the scent of strangers. And in both cases, the capacity for identification and preference is recovered when the offspring enter the post-pubertal stage.
A possible explanation for this kind of ‘rejection’ towards the body odor of one’s own adolescent children would be the prevention of incest and, therefore, endogamy.
The social nose
The sebaceous glands reach their maximum activity in adulthood. Although less intense than in adolescence, body odor still exists in each person and depends on factors such as diet, stress, hormone levels or the skin microbiome.
But what would be the point of having a changing smell throughout life if we did not have the ability to feel it? Darwin himself was wrong (no one is perfect) when he stated that “for man, the sense of smell is of very little use, if any.”
Actually, smell is effective in obtaining information of congeners, is essential when vision or hearing is restricted (dark or noisy environment) and allows detecting past events, since odor molecules persist in space and time.
Therefore, having a characteristic aroma and the ability to detect foreign odors provides social information regarding ourselves, our relatives, age, sex, personality, diseases and emotions. As in other animals, body odors help in mate selection, kinship recognition or sexual differentiation.
And what happens to our smell when we get older?
With aging, the lack of collagen in the skin crushes and reduces the activity of sweat and sebaceous glands. The loss of the former explains the difficulty of older people in maintaining thermal balance. As for sebaceous, not only does its production decrease, but its composition changes, reducing the amount of antioxidant compounds such as vitamin E or squalene.
All this, added to the lower capacity for antioxidant production by skin cells, triggers an increase in oxidation reactions, giving rise to the ‘older person’ smell, which the Japanese call kareishu.
Thus, from the age of 40, the way in which some fatty acids in the skin are processed, such as omega-7 (palmitoleic acid), begins to change. The oxidation of this monounsaturated fatty acid gives rise to 2-nonenal, responsible for the characteristic odor. By the way, this compound is also found in old beer and buckwheat, and is described as having a greasy, grassy smell.
If for some people this smell is unpleasant, most of us associate it with good memories of grandparents and parents. And it is likely that, as in childhood, it helps to perpetuate care, this time for our elders.
Therefore, the smell of old age has less to do with hygiene; In fact, 2-nonenal is not soluble in water, so it is not easily removed by showering or washing clothes.
As the skin matures, its antioxidant protection decreases, generating a greater presence of the aforementioned compound, so it is best to minimize the olfactory trail It is to drink plenty of water, exercise, follow a healthy diet, reduce stress and reduce tobacco or alcohol consumption. All of these habits reduce the oxidative stress responsible for our odor.
This article was originally published in The Conversation.
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