Study finds a link between infectious diseases and racism in the United States

New research published in the scientific journal Social Psychological and Personality Science provides evidence that the prevalence of infectious diseases plays an important role in racial prejudices across the United States.

The findings support the parasite-stress hypothesis, which holds that people exposed to diseases become more likely to adopt anti-pathogen behavioral strategies — such as avoiding and expressing more negative attitudes toward groups with dissimilar features.

“I was surprised when a 2015 study found an association between exposure to black Americans and racial prejudice, such that white individuals living in U.S. states with more black people showed increased prejudice towards this group,” said study author Brian A. O’Shea, a EU Horizon 2020 Marie Skłodowska Curie Global Fellow based in the Psychology Department at both Harvard University and the University of Amsterdam.

“The finding was counter to the extensive literature showing that contact with outgroups actually reduces prejudice. I suspected that the study was showing a spurious correlation and that perhaps infectious diseases might better explain variation in racial prejudice across the U.S. This epiphany likely occurred because I was lucky enough to have an office beside Corey Fincher while at Warwick University, who developed Parasite Stress theory, along with Randy Thornhill.”

In their study, the researchers utilized 2006-2013 data from Harvard’s Project Implicit website, a nonprofit organization that collects data about people’s automatic, or implicit, attitudes toward different groups as well as their explicit biases.

They were particularly interested in data from 355,000 white and 77,000 black respondents who completed a test of racial bias. This data was compared to disease rates across the 50 U.S. states.

The study found “that at the aggregated group level, regions with more infectious diseases are likely to have higher intergroup racial tensions,” O’Shea told PsyPost.

“Specifically, we found that if you’re a white or black person living in a U.S. state with more infectious diseases, you have a stronger feeling in favor of your in-group and/or a stronger opposition to your out-group, both consciously and unconsciously.”

“These effects occur even if we control for individual factors like age, political ideology, religious belief, education and gender, and a number of state-level factors, including median income, inequality, race exposure and more. Importantly, even within areas with high infectious diseases, there is substantial individual variation in prejudice,” O’Shea explained.

But the study only examined correlational data, preventing the researchers from establishing a causal link between disease prevalence and racial prejudice.

To further solidify their findings, O’Shea and his colleagues set up in experiment in which 588 U.S. adults completed a test of racial bias after being randomly exposed to either images related to disease, terrorism, or buildings and furniture.

White participants who showed greater aversion to germs tended to show increased explicit — but not implicit — prejudice toward black people after seeing the disease-related imagery.

“Participants who strongly agreed with questions relating to germ aversion (i.e., ‘It really bothers me when people sneeze without covering their mouths and I prefer to wash my hands pretty soon after shaking someone’s hand’) showed the highest racial prejudice, but only after they were primed with images depicting disgusting content such as mold, feces, and an individual with chickenpox,” O’Shea told PsyPost.

“We suspect that individuals with high germ aversion will be less willing to come in contact with racial outgroups, and this lack of exposure could increase racial tensions.”

“Study 2 is experimental and offers some causal evidence that reminders of infectious disease, especially among those with high germ aversion, can increase racial prejudice. More work is needed to understand why some individuals show high germ aversion, while others in the same environment are less worried when coming into contact with germs. Family upbringing and an individual’s willingness to take more risks are potentially influential factors, but this paper does not directly address this issue,” O’Shea said.

While the findings offer a new way of explaining intergroup prejudices, O’Shea said it also points to one possible way to combat them — by reforming health care.

“This research indicates that restrictions in access to health care, due to costs or lack of insurance, could have a devastating impact on intergroup relations if it leads to higher infectious disease rates. To foster the right conditions for a cohesive and integrated community, policies must be put in place to ensure vulnerable groups in society have equal access to health care,” he told PsyPost.

The study, “Infectious Disease Prevalence, Not Race Exposure, Predicts Both Implicit and Explicit Racial Prejudice Across the United States“, was authored by Brian A. O’Shea, Derrick G. Watson, Gordon D. A. Brown, and Corey L. Fincher.