The story of racial prejudice in the U.S. over the past several decades is a tale of good and bad news. On the mostly positive side, surveys of the American public suggest that overt prejudice—biases to which people are willing to admit—has been on the steady decline (although some data suggest an uptick following the presidential election of Barack Obama). On the negative side, prejudice, even in its ugliest forms, is far from eradicated. In the weeks preceding my writing of this column racial slurs surfaced on the gates of the home of basketball superstar LeBron James, and nooses were found hanging at museums in our nation’s capital.

What’s more, such overt prejudice might only be the tip of a massive iceberg. A number of prominent scholars have maintained that a good deal of racial bias has merely “gone underground,” assuming insidious forms such as implicit prejudice. Although the science of implicit prejudice is controversial, few researchers dispute that bigotry is at times manifested in subtle ways.

Against this backdrop, the concept of “microaggressions” has recently received a flurry of attention. Coined in 1970 by Harvard University psychiatrist Chester Pierce, the term “microggression” refers to a subtle slight or snub directed toward historically stigmatized individuals, especially minorities. The concept lay largely dormant until 2007, when an influential article by Columbia University counseling psychologist Derald Wing Sue and his co-authors brought it to the attention of a mainstream academic audience. According to Sue and his collaborators, the toxicity of microaggressions stems largely from their ambiguity.

To read the full article by Scott Lilienfeld, Professor of Psychology at Emory University, visit Scientific American.