A young woman illustrates behavioral immunity by isolating herself frorm everyone but a teddy bear.

Behavioral Immunity

Once again a new disease is threatening us, this time a new coronavirus. We’re familiar with this kind of threat from centuries of suffering . Still, the unfamiliarity of novelty seems to be part of what strikes fear into us. After all, the bubonic plague that once ravaged Europe is still around, but it’s no longer mysterious, and we disregard it.

Uncertainty provokes anxiety In us. Some authorities perceive a “very high” threat in today’s epidemic, while others reassure us, characterizing the threat as “low”.

This raises some interesting questions in psychology. Even the bright cookies we meet at work or in the clinic don’t handle risk judgements about viruses particularly well. Does it seem strange that we often judge risk by its scariness instead of its likelihood? So we fear getting on a plane because of terrorists but we’ll take a car onto the Interstate highway with bad brakes. Which is more likely to kill someone? How are we to judge a threat like a virus, which we can’t see?

With no consensus to rely on, it’s understandable that there’s a hot market in face masks. However, a second interesting question (beside the risk perception puzzle) lies behind people’s avoidance of anyone seen as carrying the disease. I’d bet that it’s not even a conscious decision to avoid sick people for most of us. It just seems to happen.

We all have an immune system, and by analogy our avoidance of contamination is labeled behavioral immunity. (Is it really immunity? We’ll consider that soon.)

Psychologists like Schaller have suggested that there is a behavioral contribution to immunity when we choose mates and prepare food, for example. Segerstrom, Gilbert and others use a loose interpretation of behavioral immunity to show how optimism and resilience could help us bounce back from infections.

Avoiding the threat of infection is not a knee-jerk reflex. We differ in exercising it. Would a person’s body fragrance attract or repel you? What about shaking hands? Do you prefer a fist bump? And could the ultimate in hygiene be a kiss? (Before you reply “Get out of town!”, check it out. They’re not talking liplock.)

Would fist-bumpers dump hugging into the same category as hand-shaking? Busted! (Research here.)

If only we could all get on the same wavelength

Behavioral immunity is possible because diseased people sometimes look, sound and smell different from healthy people, at least some of the time, for some kinds of sickness. This is a social signal that alerts us to the presence of disease. Maybe it attracts a caregiver’s attention, but it can also drive away anyone with a fear of contagion.

The outward appearance and inward feeling of sickness are called sickness behavior. Outwardly, it includes sleepiness, changes in skin color, and crankiness.

Someone in a protective suit stands behind a contaminated screen.

BIO: Biological immunity may present puzzles, but I think most researchers would agree that it has undergone a long period of evolution and is grounded in our genetic makeup. It’s a good starting point for a discussion of behavioral immunity.

Hank Green narrates a good introduction to a complex topic in videos here, there, and yonder. For an entertaining application to the novel coronavirus, try this podcast. If you already know all that, you can whiz through a “graduate-level” summary by Janet Tomiyama in this video. But the psychology courses I’m aware of give short shrift to the immune response, even though it’s of intense behavioral interest. Stress, acute or chronic, tends to reduce our immunity, for example. Biological immunity may give rise to some components of behavioral immunity, as well.

Biological immunity is a defense against infection, comprising well-defined responses inside the body. We inherit it in part, and learn the rest of it through experience.

PSYCHO: Acute stress activates the biological immune system to protect against infection from wounds, while chronic stress suppresses the immune system. Chronic stress actually decreases the number of white blood cells and increases an immunosuppressive mechanism in regulatory T cells. As a result, inflammation becomes more likely and so may a kind of brain fog.

If you’re free for the next few days you can catch up on all this with a long review article.

What activates the behavioral immune system? A biological answer such as disease or pathogen won’t work, because we’re unaware of microbes most of the time and we lack training in diagnosing disease.

However, we’re generally sensitive to disgusting conditions, which are often associated with dangers of contamination and contagion. Some researchers have suggested that people get disgusted by differences out of a fear of contamination and that this has protected us from new strains of disease. Disgust is a powerful emotion that bypasses intelligence to exert its effects.

This is not to suggest that disgust and behavioral immunity are necessarily conscious. We may avoid moisture without realizing what we’re doing, for example. We might shrink from someone, even a potential mate choice, without knowing why.

So how about selecting disgust as a trigger? That emotion has received considerable investigation for its value in avoiding disease and unhealthy risk, although it’s mostly learned rather than inherited (33-min. podcast). Babies have very little sense of disgust, so they pick up germs that teach their immune systems to develop.

People do vary in their sensitivity to disgusting things. You can test your sensivity here, courtesy of the BBC. I don’t know how deep the gender expectations go for tolerance of yucky stuff, but in our culture women are portrayed as more sensitive–more reliant on help to get over life’s viscous green colloids. (Is the supposed gender difference a myth? It could be that women are simply less hesitant about admitting disgust. I never noticed my wife showing as much shyness about changing diapers as I did. On the other hand, insofar as women have cooked more than men have, you’d want the person in charge of food to be pretty sensitive to rotten stuff. Funny thing is, some bacteria and their byproducts smell pretty good, even if you’re not a cheese lover.)

This is different from disgust as cultural bias and prejudice that may involve specious moral judgments*. Biologically, fear and disgust sometimes merge, as in trypophobia. But do we want to go there?

Disgust can be interesting in its own right: are there senses that don’t evoke disgust? Why isn’t kissing disgusting in our culture?

But seriously, what’s the difference between behavioral immunity and constructs like introversion, prejudice or paranoia? First, though we differ in susceptibility somewhat, behavioral immunity operates like a reflex rather than a personality quirk: It is apparently species-wide, automatic, and fixed in form. Its form consists of reduced affiliation accompanied by a perceived threat of infection. Second, it is probably a reaction to an individual rather than an outgroup. If you see someone leaving the bathroom without washing their hands, you will display behavioral immunity only toward the disease-spreading culprit you see, but not against 95 percent of humanity.

It will help to use the label precisely when you can. It’s not disgust at indiscriminate sneezing or neglectful handwashing that represents behavioral immunity, but actual behavior—avoiding  handshakes, crowds, and anyone—it’s a global problem—who eats endangered animals or sells their parts.

*This is a legit scale devised by on-the-level researchers.

SOCIAL: Our social existence brings support, cheer, and longevity. Our defense against the increased threat of disease is our behavioral immune system, often provoked into action by the disgusts we learn from others and sometimes bind us together, but varying with our kinship to others.

But did behavioral immunity evolve as a response common throughout our species? Disgust is widespread but may not be specifically guided by our genes. For now, we should look at the behavioral immune response as resembling the biological immune system but not an evolutionary extension. We will still see its many influences on our behavior when an epidemic threatens our own health.

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