A new study suggests that you can "catch" anti-black racial bias, simply from watching the way racist white people interact with African Americans.

The good news is that the opposite is true, too: The researchers found that people who observed white people's positive nonverbal acts toward black Americans become less likely to perpetuate racial discrimination.

The study was conducted by a team of researchers from Harvard, Princeton, and the University of California, and was published in May in Organizational Behavior and Human Decision Processes.

Here's how it worked: Study participants were assigned to watch one of two types of videos. In one type, white people who were highly biased against black people (according to their results on the Implicit Association Test, a measure of unconscious racial bias), interacted with black people in ways that displayed subtle expressions of negativity— not smiling, not gazing, not leaning in, etc.

In the other type of video, white people who held black people in high regard (again, according to their IAT results) did just the opposite, expressing their positive feelings in subtle ways.

After watching the videos, participants — who were mostly white — took a test to measure their racial attitudes. They rated the black Americans in the video according to how much they liked or disliked the person or whether or not they would want to be friends with him or her, and gave them scores based on six different descriptions: kind, considerate, thoughtful, hostile, unfriendly, dislikeable.

The results: The participants who watched the first type of video — the kind with subtle anti-black bias — formed more negative impressions of the black person shown in the video, adopted more negative racial stereotypes, and demonstrated greater anti-black bias themselves.

Overall, people liked and wanted to be friends with the black people who they'd observed in videos that showed them on the receiving end of subtle positive behaviors much more than they liked and wanted to be friends with black people who were on the receiving end of subtle negative behaviors.

Toxic racial bias can spread like a disease

The researchers concluded that nonverbal expressions of racial bias affect more than simply the actor and target—they affect passive, naïve observers, too.

"The results of this research suggest that racial bias can be toxic—not just for the owner and target of the bias, but for passive observers. It may indeed be the case that during everyday interactions—at work, at home, or even at the local bar’s happy hour— merely observing a biased person express subtle negativity toward a black person may be enough to shift our own racial bias," the authors wrote. " Even despite our best intentions, others’ biases may be able to creep into our minds and infect our behaviors. That simply viewing another person engaged in a discriminatory act can, without your awareness or consent, shape your own racial bias is problematic."

It's frightening to think of racism spreading this way, like an airborne disease. But the good news was that white people's positive, non-biased attitudes toward black people spread the same way.

While, as Medical Daily pointed out in its writeup of the study, the results make troubling suggestions about the power of a specific "white brand of approval," the practical implications could be powerful.

Dana R. Carney, associate professor, University of California, Berkeley's Haas School of Business, said in a press release, "What is hopeful is that our study also indicates that positive behavior toward different social groups can be contagious."

Impact on hiring

The study authors examined the results from a business perspective, and concluded that, even in organizations that consider themselves intolerant of racism, subtle expressions of racial bias from a few individuals can likely pollute the entire culture.

Of course, the opposite is true, too: "Individuals who possess and act with genuine egalitarianism and pro-black regard can actually help to shape social structure to be more equal. Authentic pro-black regard among employees in an office, for example, is therefore more than simply a ‘'good thing to have’' or the ‘'right way to be,'" they write.

They suggested future research to identify the "tipping point" at which individual racial biases start to shape a culture, and also to measure how attitudes can catch on through social networks — information that could potentially capture how to use the viral spread of racial attitudes for good.