Public figures from Hillary Clinton and actor Samuel L. Jackson to Grumpy Cat have been accused of "Resting Bitch Face." In October, behavioral researchers Jason Rogers and Abbe Macbeth published a study explaining what makes some faces particularly prone to RBF.

Resting Bitch Face has taken pop culture by storm.

Lexicographer Grant Barrett defined the term as "a face that, when at rest, looks angry, irritated or aggressive" in a 2013 New York Times wrap up of the year's linguistic zeitgeist. Barrett identifies RBF as "Dating back at least 10 years as a described concept but popularized in 2013 by a video made by the group Broken People."

While RBF is mostly credited to female celebrities, even male public figures like Kanye West have also been accused of suffering from the condition.

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Jessica Bennett described the sexist implications of of RBF and its practical use in a cultural study published by the New York Times in 2015. While RBF can help deter unwanted attention from cat-callers and amateur pick-up artists, it also implies that women who aren't smiling are being deliberately hostile.

How The Study Defined RBF

Noldus Information Technology behavioral researchers Rogers and Macbeth used facial recognition technology to investigate what distinguishes a neutral, expressionless face from a Resting Bitch Face.

"Is there something more to RBF? What is the reason that we all react to that face so negatively?" The authors asked.

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Noldus’s FaceReader differentiated eight emotions in human faces: happiness, sadness, anger, fear, surprise, disgust, contempt, and “neutral." The technology mapped 500 points on each of approximately 10,000 human faces included in the study to make each evaluation.

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Then, the researchers compared a baseline of neutral faces with photos of three celebrities who are frequently accused of suffering from RBF, Kanye West, Kristen Stewart, and Queen Elizabeth II.

What Makes A Resting Bitch Face?

The emotion most strongly linked to RBF was 'contempt', Macbeth said.

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This looked like “one side of the lip pulled back slightly, the eyes squinting a little,” Rogers asserted.

Macbeth added that other signals included "a tightening around the eyes, and a little bit of raising of the corners of the lips — but not into a smile.”

These cues are interpreted as contempt both by the Noldus machine and human brains.

However, the machine identified contempt equally in male and female faces included in the overall sample, while RBF is attributed to female celebrities far more often than male ones.

The Noldus study also stresses that the amount of contempt present in RBF isn't actual contempt, it just looks like it. "Because contempt is based upon elements of comparison and judgment, viewing this in someone’s face creates a feeling of uneasiness, or uncomfortableness, for the person viewing that face," the authors conclude.

The Sexist Stigma of Resting Bitch Face

While some people have interpreted RBF as a signal of anxiety, the most common argument about RBF is simply that the term is indicative of misogyny.

Slate's Katy Waldman asserts that RBF is a product of gendered social pressure to smile and be nice.

Studies reveal that women smile more in the office, in job interviews, and with their friends and families.

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"We’ve tangled up so many notions of gender in our smiles that the presence or absence of a grin has come to imply a distinction between male and female," she writes. "The association between smiling and keeping the peace is so sturdy that women often believe their failure to smile under certain circumstances will lead to social strain."

Women are also more likely to work in hospitality and customer service, where smiling can lead to bigger tips or better reports from supervisors.

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But the stigma of RBF can be damaging.

"Plastic surgeons say they are fielding a growing number of requests from those who want to surgically correct their “permafrowns” (again, primarily from women)" Bennett reports.

While women may be unfairly rewarded for grins, it's may be helpful to understand the expectations and behavioral cues that make RBF an object of scorn. And if you're curious, or if you think you're suffering from Resting Bitch Face? The study's authors have also invited readers to send their own photos over email for analysis.