When we feel happy, we smile. New research indicates the opposite is true, too — posing our muscles in a smile brightens our mood.

The collaborative study, described in Nature Human Behavior by an international team of researchers led by Stanford University’s Nicholas Coles, found strong evidence supporting the long-debated “facial feedback hypothesis.”

The Many Smiles Collaboration purposely included researchers on both sides of the debate. They collected data from 3,878 participants in 19 countries.

In Israel, Ben-Gurion University social-cognitive neuroscience researcher Niv Reggev and his PhD student Aviv Mokady recruited 105 BGU freshmen to do the online study.

One-third of participants were directed to hold a pen or pencil in their teeth without letting their lips touch it, thus forcing a smile.

Another third was asked to mimic the facial expressions seen in photos of smiling actors.

The final third had to move the corners of their lips toward their ears and lift their cheeks using only the muscles in their face.

In each group, half the participants performed the smiling task while looking at cheerful images of puppies, kittens, flowers and fireworks, while the other half saw a blank screen.

To measure the difference in effect, they were shown these same images (or the blank screen) again while directed to keep their facial expression neutral.

Noticeable increase in happiness

Analysis of the data revealed a noticeable increase in happiness among participants mimicking smiling photographs or pulling their mouth toward their ears. This was true no matter what country they came from.

There wasn’t a strong mood change in participants using the pen-in-mouth technique, possibly because it involves clenching the teeth and therefore isn’t an accurate analog of smiling.

“The stretch of a smile can make people feel happy and the furrowed brow can make people feel angry; thus, the conscious experience of emotion must be at least partially based on bodily sensations,” Coles said.

Reggev tells ISRAEL21c that like Coles, he was “on the fence” regarding the facial feedback hypothesis before the study. Afterward, Reggev felt “somewhat convinced that if you make people activate the right muscles it can make them happier.”

“Based on the results, which were quite robust, people should try to make themselves smile,” the Israeli social psychologist concludes.