"Keep smiling" may not be the best piece of advice or coping strategy for some people after all, suggests new research.

The researchers found that smiling frequently may actually make people feel worse if they're sort of faking it — grinning even though they feel down. When people force themselves to smile because they hope to feel better or they do it just to hide their negative emotions, this strategy may backfire.

The bottom line of the study: Whether a wide grin will hurt your emotional well-being depends on the motivation behind it, the researchers said. [Smile Secrets: 5 Things Your Grin Reveals About You]

"Most commonly, people smile when they are happy, because smiling reflects happiness," said Anirban Mukhopadhyay, an associate professor of marketing at Hong Kong University of Science and Technology. "However, people also smile when they are unhappy, to mask negative emotion or to try and become happy."

In the latter scenario, people may associate the acts of smiling not only with feeling happy, but also with feeling unhappy, he said.

In the study, the researchers conducted three experiments in which they examined how frequently people smiled and the motivation behind their expression. In one experiment, 108 people completed surveys asking them how frequently they smiled on the day of the experiment and whether they thought that people usually smile to feel good or to force themselves to feel good. The participants also completed questionnaires that examined how satisfied they were with their lives.

In another experiment, the researchers recruited a group of 63 people and showed them funny pictures, which the researchers said they were testing for use in future studies. They asked the participants to smile if they actually found the pictures funny.

And, in the third experiment, the researchers asked 85 people to list situations in which they smiled because they felt happy. The investigators asked the participants to perform facial muscular exercises in which they were told to manipulate their facial muscles to create a smilelike or non-smilelike shape. Then they examined the participants' level of life satisfaction.

When the researchers analyzed the results of the three experiments, they concluded that those people in the study who did not typically smile when they were happy felt worse when they smiled frequently, whereas the people who often smiled when they were happy felt better when they smiled frequently.

"More generally, we think that making people who are feeling bad smile could backfire and make them feel worse, because they may interpret smiling as trying to become happy," Mukhopadhyay said.

"Smiling frequently would remind them of being not happy," he said, advising that the best strategy in such cases may in fact be not to smile until the negative emotion that is making a person feel bad gets resolved.

So who should smile as much as possible and who shouldn’t?

People who smile frequently because of their naturally cheerful personality should feel free to just keep smiling, as this may indeed make them feel better, Mukhopadhyay recommended. However, people who don't naturally grin should remember that, for them, a smile is likely just "an attempt to become happy," he said.

"In practice, I think people can think about their own beliefs about smiling, see how they feel about how frequently they smile and adapt either their beliefs or their behaviors to make themselves feel better," he said.

The study was published in the July issue of the Journal of Experimental Social Psychology.

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