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Our sense of vision and smell alone are enough to make us aware that someone has a disease even before it breaks out, said the study published in the journal Proceedings of the National Academy of Sciences (PNAS).
The new study now shows that this is indeed the case.
"The study shows us that the human brain is actually very good at discovering this and that this discovery motivates avoidance behaviour," said principal investigator Mats Olsson, Professor at Karolinska Institutet in Sweden.
By injecting harmless sections of bacteria, the researchers activated the immune response in study participants, who developed the classic symptoms of disease -- tiredness, pain and fever -- for a few hours, during which 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 scanner.
They were 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.
"Our study shows a significant difference in how people tend to prefer and be more willing to socialise with healthy people than those who are sick and whose immune system we artificially activated," Olsson said.
"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 added.