Some people are comfortable going to concerts and clubs now. Others draw the line at indoor dining. And some are avoiding nearly all gatherings.

People’s assessment of what is safe has varied wildly during the Covid-19 pandemic—often leaving us baffled about why our risk decisions differ so sharply from those of our neighbors, friends and family members. Now, scientists are starting to better understand why.

Recent...

Some people are comfortable going to concerts and clubs now. Others draw the line at indoor dining. And some are avoiding nearly all gatherings.

People’s assessment of what is safe has varied wildly during the Covid-19 pandemic—often leaving us baffled about why our risk decisions differ so sharply from those of our neighbors, friends and family members. Now, scientists are starting to better understand why.

Recent research shows that, while politics and geography play a role, other factors are often more important in determining how we make decisions about Covid-19 risks. Personality traits that are shaped by genetics and early life experiences strongly influence our Covid-19-related decisions, studies from the U.S. and Japan have found.

“Personality influences how we value different possible options and their outcomes,” says Kaileigh A. Byrne, an assistant professor of psychology at Clemson University in South Carolina who studies decision-making. How we weigh risks—and the rewards we might gain from them—influences our decisions about everything from whether we exercise, go to college, or wear a mask at the grocery store during the pandemic, she says.

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In a study of more than 400 U.S. adults, Dr. Byrne and her colleagues found that how people perceive risks, whether they make risky decisions, and their preference for immediate or delayed rewards were the largest predictors of whether they followed public-health guidelines when it came to wearing masks and social distancing. These factors accounted for 55% of the difference in people’s behaviors—more than people’s political affiliation, level of education or age.

The study, which was published in May in the science journal PLOS One, surveyed participants last September and December. Dr. Byrne and her colleagues measured risky decision-making by presenting people with a gambling scenario. They could choose between two bets: One offered a guaranteed amount of money, while the other offered the possibility of a larger amount of money but also the possibility of receiving no cash. A different exercise measured people’s preference for immediate versus delayed rewards: Participants could choose a certain amount of money now, or a larger amount later. Study subjects also reported Covid-19 precautions they had taken in their daily lives, including masking and social distancing.

“People generally are more motivated by immediate gratification or immediate benefits rather than long-term benefits, even when the long-term benefits are much greater,” says Dr. Byrne. She notes that with Covid-19, people don’t feel sick immediately after an exposure so the benefits of wearing a mask, social distancing or getting vaccinated aren’t immediately apparent. “You don’t see the lives you potentially save,” she says.

Indoor dining, workout classes, concerts. These once commonplace events are coming back into daily life. But because of Covid-19, everyone now has a different level of comfort. What happens in the brain as we decide what’s risky or not? Photo illustration: Laura Kammermann The Wall Street Journal Interactive Edition

Research has also found being extroverted or introverted affects how people make decisions about Covid-19 precautions. A recent study of more than 8,500 people in Japan published in the journal PLOS One in October 2020 found that those who scored high on a scale of extraversion were 7% less likely to wear masks in public and avoid large gatherings, among other precautions. The study also found that people who scored high on a measure of conscientiousness—valuing hard work and achievement—were 31% more likely to follow Covid-19 public-health precautions.

Scientists believe that a person’s propensity to take risks is partly genetic and partly the result of early life experiences. Studies of twins have generally found that about 30% of the difference in individual risk tolerance is genetic. Certain negative childhood experiences including physical, emotional or sexual abuse, parental divorce, or living with someone who was depressed or abused drugs or alcohol are linked to risky behavior in adulthood like smoking and drinking heavily, other research has found.

And scientists have discovered that the brains of people who are more willing to take risks look different than those of people who are more cautious. In a study published in the journal Neuron in 2018 that involved scanning the brains of 108 young adults, scientists at the University of Pennsylvania found that participants who made riskier choices on a gambling task had differences in the structure and function of the amygdala, a part of the brain involved in detecting threats, and the prefrontal cortex, a region involved in executive functioning.

Even people who have the same information and a similar perception of the risks may make different decisions because of the ways they interpret the information. When public-health officials talk about breakthrough infections in vaccinated individuals being rare, for example, “rare means different things” to different people, says Jennifer M. Taber, an assistant professor of psychological sciences at Kent State University in Ohio.

During a time when differences in Covid-19 precautions are causing arguments and rifts among family and friends, knowing how people’s personalities affect decision making can ease frustrations, says Joseph W. Kable, a professor of psychology at the University of Pennsylvania and a co-author of the brain-imaging study. “It helps me have a little bit of patience and understanding” of people who make different choices, he says.

Write to Andrea Petersen at andrea.petersen@wsj.com