Thanks, Brain! An 'Internal Alarm' Warns You About People Who Are Getting Sick

Ever had that inkling that you ought to avoid a certain someone well before you even know they’re under the weather?

Well, according to science, that’s your brain doing you a solid. 

Researchers from the Karolinska Institutet in Stockholm have revealed how the brain triggers an internal alarm system of sorts when it senses soon-to-be-sick people in your vicinity.

The research team injected one group of people with harmless bacteria that set off an immune response including mild fever and fatigue (but no obvious signs of being sick) for just a few hours.

They then took smell samples from this group, as well as photos and videos, all of which were exposed to a second group. The second group was also exposed to a similar set of samples from healthy people. These participants were asked three questions: which of the people in the images and videos looked sick, which did they find attractive and which would they consider hanging out with? Their brain activity was examined via fMRI while they answered.

In the brain scans, researchers saw a signalling effect cutting across the senses when a participant looked at a photo or video of a sick person, as well as being exposed to the smell samples.

The effect is a multisensory internal alarm that tells us when someone is sick and should be averted. The answers to the questions corroborated these findings, showing that people were more likely to want to socialize with those who weren’t sick.

“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 lead investigator Mats J. Olsson of the research published in the Proceedings of the National Academy of Sciences. “We can also see that the brain is good at adding weak signals from multiple senses relating to a person’s state of health.”

h/t Forbes


After a battery of tests and misdiagnoses, I was finally diagnosed with Crohn’s Disease twelve years ago, and thus began a long battle with trial-and-error medical treatments. I changed my diet several times, even though my doctors didn’t seem confident it would change much (it didn’t), went to physical therapy for pain-related issues, and took so many different pharmaceuticals I can’t even begin to recall each and every one. My days were foggy due to side effects from pharmaceuticals, such as steroids, that made me feel worse than I did before I even took them.

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