This new study says that smiling really can make people feel happier - even if they're feeling stressed.

The paper, which was co-authored by Heather Lench at Texas A&M University and researchers at the University of Tennessee, looked at nearly 50 years of data testing whether posing facial expressions can lead people to feel the emotions related to those expressions.

"These findings address a critical question about the links between our internal experience and our bodies - whether changing our facial expression can alter the emotions we feel and our emotional response to the world," Lench said.

"These findings address a critical question about the links between our internal experience and our bodies – whether changing our facial expression can alter the emotions we feel and our emotional response to the world," Lench said.

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"Conventional wisdom tells us that we can feel a little happier if we simply smile. Or that we can get ourselves in a more serious mood if we scowl. But psychologists have actually disagreed about this idea for over 100 years" said Nicholas Coles, the lead author of the paper.

These disagreements became more pronounced in 2016 when 17 teams of researchers failed to replicate a well-known experiment demonstrating that the physical act of smiling can make people feel happier.

This new paper for Psychological Bulletin, however, describes how the team used a statistical technique called meta-analysis to combine data from 138 studies testing over 11,000 participants from all around the world. According to the meta-analysis, posing facial expressions has a small impact on our feelings.

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For example, smiling makes people feel happier, scowling makes them feel angrier, and frowning makes them feel more sad.