Smiling can trick your brain into happiness — and boost your health. A smile spurs a powerful chemical reaction in the brain that can make you feel happier. … Science has shown that the mere act of smiling can lift your mood, lower stress, boost your immune system and possibly even prolong your life

We smile because we are happy, and we frown because we are sad. But does the causal arrow point in the other direction, too? A spate of recent studies of botox recipients and others suggests that our emotions are reinforced—perhaps even driven—by their corresponding facial expressions.

Smile. Seriously, just do it. You’ll enjoy this post more if you do. (If you’re thinking “Screw that, I don’t want to enjoy this post more” then feel free to stop reading). Your smile is a powerful tool. Most people think that we smile because we feel happy, but it can go the other way as well: we feel happy because we smile.

One of the best experiments to demonstrate this came from the late ’80s. The researchers did not want to influence the results by telling subjects that the study was about emotion, so they devised an ingenious way to get the subjects to flex certain muscles of their face without knowing why.

“Some studies have not found evidence that facial expressions can influence emotional feelings,” he said. “But we can’t focus on the results of any one study. Psychologists have been testing this idea since the early 1970s, so we wanted to look at all the evidence.”

So Coles and his colleagues analyzed nearly 50 years of data from 138 studies that tried to determine whether facial expressions can affect people’s moods. The studies included more than 11,000 people worldwide.

The researchers’ conclusion: Facial expressions do have a small effect on feelings: Smiling makes people feel happier, scowling makes them feel angrier, and frowning makes them feel sadder.