The Psychological Immune System
Why seeing me sneeze makes you healthier
Posted April 4, 2010
Is it good for your health to see me coughing, sneezing and blowing my runny nose? Believe it or not, recent research suggests that the answer might be: Yes.
Of course, it's not good for your health if I sneeze right into your face. You're better off not being exposed to all those disease-causing microbes in the first place. But if you are exposed to those microbes, your immune system is going to have to fight them off; and it may fight them off more aggressively if you've just been looking at people who look diseased. That's the implication of some new results published by scientists at the University of British Columbia.
The researchers asked young adults to watch a 10-minute slide show containing a series of unpleasant photographs. Some of these participants looked at pictures of people who looked obviously sick in some way (people with pox and rashes, people coughing and sneezing and blowing mucus out of their noses).
The participants gave blood samples both before and after each slideshow. Next the researchers exposed these blood samples to a bacterial infection, and measured the extent to which white blood cells produced interleukin-6 (IL-6). IL-6 is a proinflammatory cytokine that white blood cells make when they detect microbial intruders. More IL-6 indicates a more aggressive immune response to infection. So, by measuring IL-6 before and after the slide show, the researchers were able to determine whether seeing pictures of disease-y people actually stimulated the immune system to fight infection more aggressively. And it did.
So it appears that merely looking at people who look sick does help your immune system prevent you from getting sick yourself (in another post -the Psychological Immune System 2, I discuss how thinking about illness can also lead us to think of ourselves as introverted and unpleasant, and to be quicker to make avoidant movements)
One of the authors on the article is the social psychologist Mark Schaller (we discussed his research linking disease and prejudice in an earlier post). I tracked him down in the south of France, where he's spending a sabbatical. He was willing to put aside his rigorous workload of red wine and raw sheeps-milk cheeses to answer a few questions about the research:
Doug Kenrick (DTK): I know there's lots of research showing that any kind of stressful event - even something like struggling with a difficult math problem - can trigger the immune system to work harder. How is your result different from that? What does it tell us that we didn't already know?
Mark Schaller (MS): Not all stressful events are equal in their immunological consequences. That's the neat thing that shows up in our results. We didn't just ask people to look at disease-y photos. We also had a control condition in which participants looked at photos of people who were brandishing guns (most of which were pointed right at the camera, which means they were aimed right at participants themselves). Our participants rated those guns pictures as more distressing than the disease-y pictures. But, the guns pictures stimulated barely a 6% increase in IL-6 production, which is pretty negligible. By contrast, the disease-y pictures (which, remember, were rated as actually being less subjectively stressful) stimulated a whopping 23% increase in IL-6 production. So, clearly, the story here ain't just stress. It seems that there is something specific about seeing people who look diseased that triggers the immune system to kick it into a higher gear.
DTK: So any suggestion of disease activates my immune system. That seems to make adaptive sense, no?
MS: In fact, it was a conversation with an evolutionary psychologist - Steve Gangestad - that gave me the idea to the do the study. My students and I had been doing research on cognitive mechanisms that facilitate the behavioral avoidance of disease-y people, and then I ran into Steve at a conference and he wondered out loud about the possibility of an adaptive connection between these cognitive mechanisms and the "real" immune system. So, yeah, it makes enormous evolutionary sense. Here's one way to think about it: Immunological responses sure are useful, but they come at a cost. (Inflammation ain't fun, and IL-6 doesn't grown on trees.) So it could be debilitating if your immune system was fighting infections super-aggressively all the time. Far better for you (and for your ultimate reproductive success) if your immune system was calibrated to respond selectively aggressively - to do so under circumstances in which the threat of infection seems especially acute. Here's where visual information comes in handy. If you see a bunch of people around you who look sick, that's a pretty good indicator that you're in imminent danger of infection. Which means that this is one of those times when it'd be wise to allocate more of those precious bodily resources to mount an especially vigorous immunological defense.
DTK: It's one thing to show that visual information somehow triggers a more aggressive immune response. It's another thing entirely to explain exactly how it does it. What's the mechanism?
MS: That's an interesting question, and to be honest, we really don't know the answer. In our article, we offer some speculations about how subjective appraisals of threat trigger the production of hormones, such as cortisol and norepinephrine, that bind to receptors on immune cells, and about how parts of the sympathetic nervous system connect the brain to lymphoid organs, releasing neuropeptides and neurotransmitters that modulate immune function. I won't bore you with the details because, frankly, that's not my area of expertise (or to put it less generously: I'm a total moron about stuff like that, and I'm just lucky to have colleagues like Greg Miller and Edith Chen, who aren't). The bottom line is that there are lots of neurochemical pathways that allow the things going on in our big brains to exert an influence on immunological defense, but we just don't know what specific mechanisms are involved in this specific effect. It's an important topic for future research.
Schaller, M., Miller, G.E., Gervais, W.M., Yager, S., & Chen, E. (2010). Mere visual perception of other people's disease symptoms facilitates a more aggressive immune response. Psychological Science, 21, In press.
For a discussion of related research, see The Psychological Immune System 2.