There's nothing wrong with smiling, but telling someone to smile probably won't make them happy.

"Telling anybody to do anything can rub you the wrong way, particularly if it’s not natural to you," said biological anthropologist Helen Fisher.

Women know this, because when a woman isn't smiling, people notice. Some female celebrities who don't smile often, like Kim Kardashian, have publicly commented on their choice not to smile. Men often don't face the same criticisms.

During Hillary Clinton’s campaign, plenty of men told her she needed to smile.

(Steve Clemons later apologized.)

Fisher, who's studied and written about women's changing roles in society, said men might tell a woman to smile for one of two reasons: they are caring or they are controlling. While the first might be well-intended, neither will probably be well-received.

"If you tell someone who is always sullen that they might get along better with their workmates if they smile more…it might be a sign of affection," Fisher said.

On the other hand, a lot of men view smiling as subservient, weak and vulnerable. In fact, Fisher said, high-testosterone men do not smile much, and overall use less facial expression. So, telling a woman to smile might be pushing her back into a traditional stereotype.

And, why do women always need to look happy anyway? One Indianapolis Star reporter wrote an entire column on the topic, saying she doesn't feel the need to smile all the time and there's nothing wrong with that.

"I do not always feel the need to be more attractive," Leslie Bailey writes. "I don't always want to look approachable."

Brooklyn-based artist Tatyana Falalizadeh started an art project titled Stop Telling Women to Smile, which shows telling a woman to smile can be seen as harassment.

Even if a comment encourages a woman to smile more, it's likely they will pick up a fake smile, Fisher said.

"If people tell you to smile when you don’t feel like smiling, [and you smile] you aren’t being true to yourself," she said.

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