When it comes to detecting and avoiding illness in others, it turns out the nose knows.
A team of scientists led by professor Mats Olsson at the Karolinska Institutet in Sweden has discovered that the human brain is better at recognizing and avoiding disease in others than previously thought. Their latest findings showed that our eyes and nose can make us aware that someone has a disease before symptoms become apparent, and our brain acts on this information to avoid those people.
To study this phenomenon the research team injected enough harmless bacteria to activate immune responses for a few hours in the participants, who then developed classic cold symptoms of fatigue, pain and fever. They were then photographed and filmed and had smell samples taken from them. Another group of participants was exposed to the smells and images from the first group alongside images and smells from a healthy control group and asked to rate how much they liked the people while hooked up to an MR scanner.
"Our study shows a significant difference in how people tend to prefer and be more willing to socialize 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."
The researchers consider this biological confirmation of the argument that survival naturally entails avoiding infection. Since combating disease takes a lot of energy, avoidance is our first line of defense and part of our basic survival instinct.