The human brain is better than previously thought at discovering disease in others even before it breaks out, thereby helping us avoid sick people, a new study has found.
Our sense of vision and smell alone are enough to make us aware that someone has a disease even before it breaks out, researchers said.
By injecting harmless sections of bacteria, researchers from Karolinska Institutet in Sweden activated the immune response in participants, who developed the classic symptoms of disease - tiredness, pain and fever - for a few hours.
During that time smell samples were taken from them and they were photographed and filmed. The injected substance then disappeared from their bodies and with it the symptoms.
Another group of participants were then exposed to these smells and images as well as those of healthy controls, and asked to rate how much they liked the people, while their brain activities were measured in a magnetic resonance (MR) scanner.
The group was then asked to state, just by looking at the photographs, which of the participants looked sick, which they considered attractive and which they might consider socialising with.
"The study shows us that the human brain is actually very good at discovering this and that this discovery motivates avoidance behaviour," said Mats Olsson, professor at Karolinska Institutet.
"We can also see that the brain is good at adding weak signals from multiple senses relating to a person's state of health," Olsson said.
The study was published in the journal Proceedings of the National Academy of Sciences (PNAS).
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