In 1934 a British physicist named BA McSwiney lamented in front of his colleagues at the Royal Society of Medicine that most doctors were not interested in the chemical composition of human sweat.
His only focus of attention at that time was the mechanism by which the evaporation of sweat from the surface of the skin served to cool the body itself.
But McSwiney knew there was something else. What kind of substances left our body with sweat? Those losses were good or bad?
Substances that leave us with sweat
A person sweats every day the liquid equivalent to 600 or 700 cubic centimeters .
In that sweat there are chlorides, urea – the substance that gives the name to urine – and ammonia. In addition there are proteins, sugars, potassium and bicarbonate.
And also remains of metals such as zinc, copper, iron, nickel, cadmium, lead and even a little manganese.
Sweating is an important mechanism for the body to expel some of those metals.
But not all the things that leave our body in sweat have a chemical nature.
Everyone has ever started to sweat after eating something very spicy, and most people are familiar with emotional sweating due to fear, shame, anxiety or pain.
The palms of the hands, forehead and soles of the feet are associated with emotional perspiration .
It is there that the eccrine sweat glands, which are distributed in millions throughout most of the body, are crowded in a much denser way. Other parts of body has apocrine glands are found under the armpit and groin area which cause sweating around the female vagina and sweaty testicles.
For example in those areas there are up to 700 glands per square centimeter of skin , while in the back there are about 64.
The truth is that sweat induced by the emotional is an important communication tool.
In fact, the smells that we detect in sweat can tell us a lot about how the other feels.
Fear through the smell
In an experiment at the University of Urecht, in the Netherlands, a group of psychologists collected sweat samples from men while watching scenes from selected films to evoke feelings of fear or disgust.
Then they asked 36 women if they could detect any emotional clues in the sweat samples.
The researchers found that when women were exposed to the sweat samples derived from the emotion of fear their own facial expressions reflected fear as well .
And when they were exposed to the samples derived from the feeling of disgust, they also imitated that emotion facially.
On the contrary, when the participants smelled the samples that served as control, they did not show any predictable facial expression.
This finding made researchers think that sweating is an effective mechanism to transmit an emotional state from one person to another .
It is also important to emphasize that the facial expressions that women made while smelling the sweat samples had no relation to their subjective perception of the intensity or liking of the smell.
So they could show an aspect of disgust even when they said that a particular sample had a pleasant smell.
In other scientific studies similar patterns of behavior have been found.
A state of “contagious” alert
For example, in 2012 psychologists and psychiatrists at the State University of New York extracted sweat samples from the t-shirts of 64 donors.
Half had jumped free from an airplane for the first time while the other had exercised a lot.
They then asked volunteers to smell the sweat samples before showing them angry faces.
And they discovered that those who smelled the sweat of the terrified paratroopers later were alert to the unfriendly faces, but also to the neutral or ambiguous ones.
The psychologists described it as surveillance: the sweat produced by the sensation during the free fall induced the participants to pay attention to any social clue, however subtle it might have been in other circumstances .
On the contrary, those who smelled the sweat of the participants who had exercised were only alert to see the angry faces, as would be normal in any circumstance.
Another experiment by German psychologists and neuroscientists found that the sweat extracted from men in a state of anxiety, who participated in a high-risk sports course, made women who smelled the samples take riskier decisions.
That after spending some time calibrating the different options, in a computer game designed to assess the behavior in risk taking.
An ancestral advantage
None of these studies indicates whether people were aware that another person’s sweat had altered their own behavior.
But they do suggest that sweat can, at least in some cases, communicate important information about our mental state.
They also suggest that we use the information that contains the sweat of another person to better understand what surrounds us .
Our species has adapted to verbal and linguistic communication, but language is a relatively new tool in our social evolution.
It seems reasonable to imagine that our ancestors used for their benefit the olfactory information that passed through their noses and that that ability reached us.
In addition, seeing that someone sweats can allow people to perceive the intensity of an exposed emotion.
Sweat, in other words, can be much more than a stinking excretion.