Humans guard against illnesses by avoiding those who look or act sick. But how does that "behavioral immune system" contend with pandemics like coronavirus, which can spread without symptoms?

Pathogen-avoidance psychology describes how people detect and react to cues of infection risk.

"You may experience anxiety or in certain contexts you might experience disgust. That's really tied to this idea of preventing infection, because the kinds of things that we become disgusted by are those that are highly pathogenic," said Joshua Ackerman, an associate professor of psychology at the University of Michigan.

But those traits evolved before humans built civilizations that spawned pandemics, and tend to focus on symptoms like sneezing, coughing or open sores.

In an opinion piece in the journal Trends in Cognitive Sciences, Ackerman explains why those instincts fare poorly against COVID-19, which requires people take precautions against germs, which are effectively invisible, and to trust experts' say-so over their own sensory input.

"We know that there is a misfit between what people are designed to look for and what's actually dangerous," he said.

The global spread of coronavirus has raised interest in the psychology of infectious disease responses, inspiring some to turn to frameworks like pathogen-avoidance psychology.

But pandemics often don't work like typical bugs. Cholera only causes symptoms in 1 in 10 cases, and shunning symptomatic people does little to guard against the disease. That's because cholera spreads through the consumption of cholera bacteria, often via shared water supplies tainted with fecal matter.

"As researchers, if we're misapplying these ideas, then they're going to lead to mistakes in how we do the research and maybe misunderstandings of what the results of that research actually mean," said Ackerman.

Ackerman fears such muddles could further erode public trust in science at a time when effective containment and response depend on it.

They could also lead experts to waste time, energy and resources on the wrong interventions.

As for COVID-19, Ackerman says he does not know of a current model that quite captures its nuances. The closest analogue he and his colleagues could manage was an admittedly imperfect one: radiation from nuclear fallout.

"It's not a threat that is like a wild animal or a dangerous person that might be chasing after you. Instead, it's a threat that exists in a place and can be spread through nonobvious means."