People’s ability to use smell and vision to detect and avoid others who are sick is better than believed, a new study suggests.
Researchers injected harmless bacteria into volunteers, to trigger classic symptoms of illness such as tiredness, pain and fever. These study participants were photographed and filmed, and odor samples were taken from them.
Another group of people were given brain scans while they were shown the images and exposed to the odor of the “ill” group along with a “control group” of healthy people. These volunteers were then asked to identify which people in the two groups looked sick, which they considered attractive and which they might socialize with.
“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,” said principal investigator Mats Olsson. He is professor in the department of clinical neuroscience at the Karolinska Institute, in Sweden.
“We can also see that the brain is good at adding weak signals from multiple senses relating to a person’s state of health,” he added in a Karolinska news release.
The findings provide biological confirmation that survival naturally entails avoiding infection, the study authors said.
“Common sense tells us that there should be a basic behavioral repertoire that assists the immune system. Avoidance, however, does not necessarily apply if you have a close relationship with the person who is ill,” Olsson noted.
“For instance, there are few people other than your children who you’d kiss when they have a runny nose. In other words, a disease signal can enhance caring behavior in close relationships. With this study, we demonstrate that the brain is more sensitive to those signals than we once thought,” he concluded.
The study was published online recently in the Proceedings of the National Academy of Sciences.
The World Health Organization has more on infectious diseases.