Top highlight How Your Brain Prevents You From Getting Sick

Have you recently dodged a person sneezing at the store by instinct or automatically taken a few steps back when you pass someone without a mask on? These behaviors could be part of an adaptive response evolutionary psychologists call the “behavioral immune system.”

Your behavioral immune system causes you to adopt a cognitive bias against things that could hurt you and then motivates protective behaviors. Think of it as your first line of defense — your brain’s way of trying to prevent your physiological immune system from ever having to kick into gear. The behavioral immune system is basically your nervous system’s goal to avoid potentially debilitating side effects of the physiological immune response, like a fever or fatigue, and all the health risks that could come with being infected by a parasite.

“We all have behavioral repertoires we do to avoid being in contact with pathogens or people who could be sick.”

Nate Pipitone, PhD, an evolutionary psychologist who teaches at Florida Gulf Coast University, says the behavioral immune system is made up of primarily automatic and instinctive reactions, an extension of the autonomic nervous system. “Most of these behaviors aren’t higher-level thought processes — instead, they manifest automatically through more primitive processing. Your cognitive processes allow you to justify what you’re doing after the behavior.”

While self-protective behaviors like avoiding people who could make you sick are a major way human ancestors survived over time, experts think these unique, self-protective behaviors will be even more pronounced during and even after the pandemic. “We all have behavioral repertoires we do to avoid being in contact with pathogens or people who could be sick,” says Pipitone. “And they’ll start to manifest even more thanks to Covid-19.”

The brain’s way of engaging in preventative medicine

In a 2011 article in Scientific American, evolutionary psychologist Mark Schaller described the behavioral immune system as the human brain’s way of engaging in preventative medicine. “It’s a suite of psychological mechanisms designed to detect the presence of disease-causing parasites in our immediate environment, and to respond to those things that help us to avoid contact with them,” he writes.

One way the behavioral immune system surfaces is the experience of disgust: being revolted by and physically avoiding things that could make you sick. Commonly, according to research, people experience “pathogen disgust,” where they’re grossed out by small animals like rodents and spiders that historically have transmitted diseases to people (like during the Bubonic plague).

Of course, we’re also disgusted by people when our brain perceives them as potential infectious agents: One study shows people are commonly disgusted by the violation of hygiene norms, like body odor, and visually disgusting things, like infected wounds filled with pus.

During Covid-19, this type of behavioral immune response shows up most clearly when people are disgusted by and avoid obviously sick people or steer clear of someone who’s more likely to give you the virus (like your neighbor who hosted a barbecue last weekend).

Other behaviors might be more subtle. Marianna Strongin, PhD, a clinical psychologist in New York, says several of her patients have noticed themselves automatically holding their breath when they walk near people on the sidewalk. Other patients who haven’t had Covid-19 are developing suspicion toward activities like ordering takeout, which could involve contact with an unfamiliar person or their germs. “I have one client who has only eaten at home during the pandemic, and since she’s been healthy, she now thinks restaurants are threatening,” Strongin says. (Luckily, it’s possible to order takeout safely with the right precautions.)

Interestingly, research shows in addition to preventing contact with ill individuals, these behaviors may actually motivate the physiological immune response. One study showed that when people experience disgust (specifically due to the threat of infection), their saliva had more markers of immune function. Another experiment found that merely watching someone sneeze can trigger higher white blood cell activity.

The downsides of the behavioral immune system

Just as the physiological immune system can take a toll on the body with potentially uncomfortable symptoms of an immune response (think fever, fatigue, etc.), Schaller theorizes that the behavioral immune system can compromise social relationships. It may cause you to avoid social situations, which could lead to self-isolation and loneliness (even when social distancing isn’t required, like during a pandemic).

In other situations, there might be harm to others. For example, experts say that the behavioral immune system can cause hesitation about unfamiliar people, which may surface as xenophobia or cultural stereotypes. One study found prejudice was heightened in people who perceived themselves to be more susceptible to infection. “Under ancestral conditions, strangers were probably part of a competing tribe who could threaten your resources or introduce a novel pathogen to your tribe,” says Glenn Geher, PhD, an evolutionary psychologist and professor at the State University of New York, New Paltz.

During Covid-19, this type of behavioral immune response shows up most clearly when people are disgusted by and avoid obviously sick people.

A perpetual hyper-vigilance, even after Covid-19

Schaller writes in Scientific American that since it’s impossible to detect every person who could infect you, the brain likes to err on the side of caution. Think of the behavioral immune system like a smoke alarm: You’d probably rather have an over-functioning one than one that beeps when you’re cooking than one that’s out of battery when your kitchen is full of smoke.

Pipitone predicts this type of hyper-vigilance, from mask-wearing to hesitation about physically touching another person, could stick around long after the threat of the SARS-CoV-2 virus, maybe even years. While it might be annoying to think twice about getting together with a friend or hugging a neighbor, these behaviors are some of the best evidence that your brain is bent on surviving.

If your hypervigilance leads to isolation or anxiety and continues even when the threat of Covid-19 subsides, consider seeking support. Strongin says early intervention is key — seeking mental health treatment or physically distanced social connection during the threat to reduce stress. “People are being told the world is a scary place right now, and it’s harder to undo those beliefs once they set in,” she says. “So it’s important to seek support now before those beliefs begin to seep into people’s long-term behavior.”