Your Brain Knows When Other People Are Sick Before You Do

Korin Miller
Your brain can subconsciously identify someone who is sick before the symptoms are as obvious as this. (Photo: Getty Images)
Your brain can subconsciously identify someone who is sick before the symptoms are as obvious as this. (Photo: Getty Images)

It makes sense that you would want to keep your distance from someone with obvious signs of a cold, but new research has found that your brain is subconsciously aware of when someone is in the early stages of an illness — even if it doesn’t actually register with you.

The study, which was led by Sweden’s Karolinska Institute and published in the scientific journal Proceedings of the National Academy of Sciences, discovered that a person’s sense of sight and smell alone are enough to raise a red flag that someone is ill even before that person shows obvious signs of being unwell. And, the study found, people tend to avoid sick people because of it.

For the study, researchers injected people with harmless bacteria to activate their immune response. The participants developed fatigue, pain, and fever for a few hours, and smell samples were taken from them, as well as pictures and video. After a little while, the symptoms disappeared.

Researchers then took another group of people and exposed them to the smells, photos, and video of the “sick” people, who were mixed in with smells and images of healthy people. Scientists then asked them to rate how much they liked the people, who they thought was attractive, and who might they like to hang out with, while their brain activities were monitored with an MRI scanner.

Here’s what they found: Participants were less likely to say they wanted to hang out with those who were sick, and the body odors from sick people tended to make them even less likable. Researchers say this suggests that the brain is good at adding together weak signals from multiple senses to help determine when someone is unhealthy.

They also point out that, while your immune system is generally good at fighting off illness, it takes a lot of energy to keep you healthy — and that can explain why your brain wants to detect illness in others early and send you running in the other direction.

But there’s a more compassionate side to this too: Women’s health expert Jennifer Wider, MD, who did not work on the study, tells Yahoo Beauty that it could help people better care for their loved ones. If someone close to you has a cold or flu, getting a sense that they’re sick early on could prompt you to provide supportive care or, at least, some sympathy.

And if they’re starting to suffer from a more serious illness, your early awareness of it could help prompt them to seek medical intervention, which could have big implications for their prognosis. “The ability of loved ones spotting early signs of disease in their significant others can have a significant positive impact on early diagnosis, which offers a much better prognosis for many diseases,” Wider says.

Regardless of what you detect in the people around you, it’s pretty amazing that your sight and smell can pick up on illness before you’re even conscious of it.

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