The Sight Of You Sets Off Alarm Bells

This just in: taking a glance at someone who doesn't look well may trigger your immune system to go on the alert. So says a new study on the subject that was conducted by researchers at the University of British Columbia.

Grossed Out

There have been many studies on the subject of visual cues and illness. As a result, we already knew that the inclination we have to back away when we see someone having a coughing fit or the squeamish, grossed-out feelings that are generated when we see infections such as boils and rashes serve as a biological defense to keep down the spread of infectious diseases. But the researchers at UBC wanted to see if that reaction goes deeper than just a sort of primal disgust that makes us turn away.

To that end, the team gathered 28 people to perform a unique study. Some of the subjects were made to watch a slide show of images related to infectious conditions such as sneezes and skin lesions. Other participants watched a slide show depicting pieces of furniture. The scientists took blood samples before and after the participants watched their respective slide shows.

In those who watched the slide show of disease images, blood samples revealed that the participants' white blood cells were manufacturing more pro-inflammatory cytokine interleukin, which acts as a stimulant for the immune response. Those who looked at the furniture images showed no such increase.

Threatening Stimuli?

To double-check that the response was not set off by some other threatening stimulus, the team did a follow-up study in which half of the participants were shown images of disease and the other half were shown images of marksmen aiming firearms at the viewers. Those who watched the images of disease had that same boost to their immune systems as in the earlier experiment while those who looked at the gun/marksmen images did not. The study authors commented, "These results provide the first empirical evidence that the mere visual perception of other people's disease symptoms can cause the immune system to respond more aggressively to microbial stimuli connoting infection."

But the scientists add that this may not be such a positive event since in larger populations, it's possible to be exposed to myriad infectious disease visual cues even when the threat for these conditions is minimal. The resulting frequent boosts to the immune system can be tough on the human body. "The immune system may often be primed to respond aggressively to infection even under conditions in which there is no imminent threat of infection. Persistent priming of immune responses can have detrimental effects on individuals' immune functioning," say the researchers.