April 28th, 2010
12:28 PM ET

Sight of sick person can trigger immune response

By Elizabeth Landau
CNN.com Health Writer/Producer

You may cower in disgust when someone sneezes near you, but just seeing that person may make your immune system prepare for battle, a new study suggests.

Research published in the journal Psychological Science found that when people viewed a slide show of photos depicting symptoms of infectious disease - pox, skin lesions, sneezing – their immune response became more aggressive against bacteria. The study was led by Mark Schaller at the University of British Columbia.

One group of participants viewed a slide show of furniture followed by the disease slideshow in a separate session, and the other group saw the furniture photos and then, on a later occasion, images of people holding firearms. Everyone involved had blood samples drawn before and after viewing the slideshows.

Scientists compared the white blood cells of participants who viewed the disease slide show against those who saw the gun depictions. They found that the white blood cells of people who saw the disease images tended to respond more aggressively to bacteria than the group that saw the guns.

Researchers also looked at emotional state, and found that participants’ stress levels were higher after the firearms presentation than after the infectious disease images. Similarly, they found that the level of participants’ disgust with the pictures of ill people did not have an effect on the immune response.

This suggests that even though the firearm slide show was more stressful, but also depicted a threat, the immune reaction was not as aggressive as with the infectious disease images, the authors wrote.

The study, while small at 28 participants, is the first empirical evidence linking visual perception and immune system aggressiveness in the presence of bacteria, the authors wrote.

Having this immune response may have had its advantages in the days of early humans - even though they may have recoiled at the sight of other sick people too, their immune responses would have helped them live in proximity with others. But this phenomenon may also have disadvantages, the authors note. A 2004 study in Psychological Bulletin, led by Suzanne Segerstrom at the University of Kentucky, suggested that persistent priming of the immune system could have negative effects overall.

“The overall implication is that the link between perceived disease cues and immune responsiveness may have important consequences for human health and welfare,” the authors of the new study wrote.

Editor's Note: Medical news is a popular but sensitive subject rooted in science. We receive many comments on this blog each day; not all are posted. Our hope is that much will be learned from the sharing of useful information and personal experiences based on the medical and health topics of the blog. We encourage you to focus your comments on those medical and health topics and we appreciate your input. Thank you for your participation.

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soundoff (67 Responses)
  1. RA

    n=28 is all it takes to get published in Psychological Science? Immunologists would have a field day with these "findings".

    April 28, 2010 at 18:28 | Report abuse | Reply
  2. Kim

    I haven't been sick in years and I think it's partially due to fleeing when around sick people. I don't stay just for the sack of not making the situation awkward when someone starts coughing up a lung. I leave. Haven't gotten 1 cold, sore throat, runny nose, or flu in 2 years.

    April 28, 2010 at 19:16 | Report abuse | Reply
  3. Nancy

    That was a bad choice for a control. It is known that stress suppresses the immune system, so it can't be concluded that the sneezes increased immune responses because maybe the guns decreased them.

    April 28, 2010 at 19:23 | Report abuse | Reply
  4. Mark

    Interesting article. Getting a little sick however of the way everyone with a study feels the need to give evolution a reach around no matter how big a stretch it is. If you want fame or funding these days you have to be able to tie your work in with either defending evolution or defending against terrorism.

    April 28, 2010 at 20:22 | Report abuse | Reply
  5. Brandon

    Very interesting study. I've often wondered if certain things will help to boost the immune system. Throughout my childhood I always got some crap for biting my fingernails. I never got sick more than the next kid, and I started telling people that the small yet consistant introduction of bacteria to my body helped prepare and strengthen my immune system. I usually just get a laugh out of it, but recently I started wondering if that actually has any merit.

    April 28, 2010 at 20:32 | Report abuse | Reply
  6. A. Pace

    Excellent stuff. A microbe responds to environmental stimuli using phosophorelay systems to elicit a cellular response, just as humans do with their senses. So why can't the downstream effect function in the immune system? The metabolic cross-talk that must occur for this sort of process must be amazing; i'd say too complex for today's biochemistry, and better sequencing technology might not be the savior.

    Basic science will play a crucial role in uncovering some amazing things about the human body in the next century. Keep the funding coming!

    April 28, 2010 at 22:27 | Report abuse | Reply
  7. GA

    Could you provide a reference for the following or describe what the negative effects are?

    "A 2004 study found that persistent priming of the immune system could have negative effects overall."

    April 28, 2010 at 23:20 | Report abuse | Reply
  8. Peter

    This study is false. Increased levels of stress and cortisol inhibits the immune system. So it was not that watching a disease slide show caused an increased immune response. Rather, the comparison group who saw stressful images had a depressed immune system, making it look like the other group had an "enhanced" immune response.

    April 29, 2010 at 01:29 | Report abuse | Reply
  9. Chris

    The article notes that "participants’ stress levels were higher after the firearms presentation than after the infectious disease images." It would seem that all they really proved is that stress depresses the immune response (via cortisol), which is already well-known. Did they not have a control that didn't cause stress? Otherwise they don't have a good baseline against which to show that viewing the pictures of ill people actually *improved* immune response.

    April 29, 2010 at 01:52 | Report abuse | Reply
  10. Roman

    Can we please get name of the authors or title of the original study?

    April 29, 2010 at 02:02 | Report abuse | Reply
  11. dan the man

    my questions are, of the study participants how many got sick after the immune system boost? also how can you measure a normal immune system? Is there such a thing? equality in humanity does not exist on the cellular level

    April 29, 2010 at 02:03 | Report abuse | Reply
  12. elandau

    Thanks for your interest; I have updated the post with further citation information, but for quick reference, this is the study:

    Schaller, Mark, et al. (2010) "Mere Visual Perception of Other People’s Disease Symptoms Facilitates a More Aggressive Immune Response." Psychological Science.

    And the one mentioned further down is:

    Segerstrom S.C., Miller G.E. (2004). Psychological stress and the human immune system: A meta-analytic study of 30 years of inquiry. Psychological Bulletin, 130, 601–630.

    April 29, 2010 at 08:50 | Report abuse | Reply
  13. Susan R. Rabinowitz, NoEvidenceOfDiseaseBook.com

    Do we unconsciously respond to someone sneezing near us? I didn't pay much attention, at least consciously to a sneeze until my immune system was compromised due to lymphoma. Could it be so simple as to merely look at photos of people sneezing to improve our immune systems? That would be the most natural and in-evasive way to go!

    April 29, 2010 at 09:04 | Report abuse | Reply
  14. Stress

    A few posts have suggested that these findings are "false" on the basis of the idea that stress inhibits immune functions via cortisol. In fact, the story is much more complicated than that. Whether stress leads to increases or decreases in various immune system activities depends on many factors – the duration and intensity of the stressor, the type of hormone responses it elicits, and the kind of immune function being considered. The paper by Segerstrom in 2004 provides a good overview of these patterns. Also, cortisol's effects on immune functions are not uniformly suppressive – at low physiologic doses it mostly has enhancing effects – but this too depends somewhat on which immune process is being considered.

    April 30, 2010 at 14:25 | Report abuse | Reply
  15. scol

    When my spouse knows someone is sick, it bothers him so much that he is usually sick within 2 or 3 days. I don't tell him if the kids and I are not feeling well, because I know he will make himself ill.

    May 7, 2010 at 21:30 | Report abuse | Reply
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Get a behind-the-scenes look at the latest stories from CNN Chief Medical Correspondent, Dr. Sanjay Gupta, Senior Medical Correspondent Elizabeth Cohen and the CNN Medical Unit producers. They'll share news and views on health and medical trends - info that will help you take better care of yourself and the people you love.