Is faking a smile good for you? Since Charles Darwin published a book on the subject in 1872, there has been debate.

Darwin said that the free expression by outward signs of an emotion makes it more intense.

The idea has persisted because of popular culture. Nat King Cole wrote a song called "Smile" in which he said, "If you just smile, life is still worthwhile."

Does this idea stand up to scrutiny? A 1988 study asked people to hold a pen with their teeth in order to make them smile.

When shown a cartoon, smiling without being aware of it made people feel funnier.

The data from 17 studies that used the pen-in-mouth trick could not be compared to the original findings.

Over the years, researchers have done various studies to find out how writing on our faces affects our moods. The effect of smiling was only small according to a review of 138 studies.

Researchers have recruited thousands of people from all over the world to put this smiling effect to the test.

The study asked volunteers from 19 countries to smile or maintain a neutral expression and then rate their happiness.

If volunteers were aware of what the researchers were doing, they would rate the interventions more favorably. The researchers came up with a way to get volunteers to leave the scent.

They issued decoy instructions such as "Place your left hand behind your head and blink your eyes for 5 seconds" and pretended to be studying how small movements affect math-solving abilities.

There were three smiling interventions mixed in with the decoy tasks.

Volunteers had to hold a pen with their lips for one of the tasks. A cartoon was not used and happiness was measured instead of amusement at the end of the study.

Volunteers mimicked a picture of an actor smiling or blank expression.

Researchers asked participants to put on a happy expression by either moving the corners of their lips toward their ears or maintaining a blank face.

Participants completed a simple math problem, a happiness and anxiety questionnaire, and an anger, tiredness, and confusion survey after completing the decoy tasks.

The effect of the pen-in-the-mouth task on feelings of happiness was less than in the facial action and mimicry tasks.

The researchers say that facial feedback can amplify ongoing feelings of happiness but also initiate feelings of happiness in otherwise neutral contexts.

It's possible that an active task such as mimicking a facial expression was less boring than a passive task.

The researchers compared the neural expression tasks against the decoy tasks. It was shown that smiling had more of an impact on happiness than other activities.

During the experiment, half of the participants viewed a series of upbeat images. The effects of smiling on happiness were tested.

There was a happiness effect in both the presence and absence of emotional stimuli.

According to the researchers, faking a smile could affect our moods because people assume that we are happy because we smile.

Can you smile for five seconds in the morning? That is still questionable.

There is a chance that small facial feedback effects could accumulate into meaningful changes in well-being over time.

The effect of positive images on happiness has not emerged as a serious well-being intervention, so it's not likely that facial feedback interventions will either.

The paper was published in a journal.