Can a smile make you happy? In a famous study in 1988, people held a pen in their teeth. This made their faces look like a smile. They thought cartoons were funnier.

But in 2016, 17 labs tried the same test, and the result was almost zero. Later, a study in 19 countries found that making a smile can make people a little happier.

The facial feedback hypothesis says that our facial expressions can affect our feelings. A famous 1988 study tested this cleverly.

Participants held a pen either in their teeth, which forces a smile, or in their lips, which prevents one. Those who held it in their teeth rated cartoons as funnier. The study appeared in textbooks for years.

However, in 2016, 17 labs repeated the experiment with about 1,900 people and found almost no effect. The story did not end there. In 2022, researchers in 19 countries tested three ways of smiling. The pen method gave no clear answer, but copying a smile or smiling on purpose made people slightly happier.

"We don't laugh because we're happy; we're happy because we laugh." This old idea, the facial feedback hypothesis, gained scientific fame from a clever 1988 experiment. Participants held a pen either between their teeth, forcing a smile-like expression, or between their lips, preventing one, without being told the true purpose. The "smiling" group rated cartoons as funnier, and the finding spread through textbooks and self-help books.

During psychology's replication crisis, however, 17 laboratories conducted a preregistered replication with about 1,900 participants in 2016 and found essentially no effect. The original lead author objected that participants in the replication had been video-recorded, and a 2018 Israeli study indeed found the effect only when participants were not being filmed, although that study was small. A 2019 meta-analysis of 138 studies then concluded that facial feedback effects exist but are small and variable.

In 2022, the Many Smiles Collaboration, involving researchers from 19 countries, including both supporters and skeptics, tested about 3,900 people. The pen method produced inconclusive results, but mimicking smiling faces or voluntarily smiling slightly increased happiness. Even so, participants may have guessed the purpose of the study, so part of the effect could reflect their expectations rather than their faces.