Can faking a smile make you feel happier?

When you're feeling down and don't have time for your typical pick-me-ups, you may follow the classic advice to fake a smile to trick yourself into happiness.

But can forcing a smile actually cheer you up?

The question has been controversial among scientists, Marie Cross, an assistant teaching professor of biobehavioral health at Penn State, told Live Science. But in the past few years, research has revealed what she said feels like a clear answer: At least in a laboratory setting, making yourself smile can improve your mood.

A 2019 meta-analysis published in the journal Psychological Bulletin found that grinning could not only amplify happiness but create it.

"This is like the difference between smiling while looking at a picture of a puppy and smiling while staring at a blank wall," said Nicholas Coles, a research scientist at Stanford University who investigates emotions and lead author of the study. "It appeared that smiles could not only increase how happy you felt about the puppies but could also make you feel happy in an otherwise neutral context where you have no actual reason to feel happy."

Related: What happens in our brains when we 'hear' our own thoughts?

However, the meta-analysis findings weren't strong, Coles said, because it was based mostly on old, questionable research. "There's an analogy in meta-analysis called crap in, crap out. And unfortunately, you don't know if the previous evidence is crappy or not," he told Live Science, because you can't talk to the scientists who found it.

Moreover, a high-quality paper published in the journal Perspectives on Psychological Science in 2016 came to a conflicting conclusion when it failed to replicate a seminal study's findings.

Based on these two factors, Coles wasn't entirely sold on his own review's findings. So he gathered an international team of researchers with differing viewpoints on the subject, dubbed The Many Smiles Collaboration. They designed a study, published in Nature Human Behaviour in 2022 that looked at more than 3,800 participants from 19 countries.

For the study, the researchers had participants pose a smile in three different ways: by looking at a photo of a smiling person and copying their expression, by following muscle-by-muscle instructions on how to smile, or by holding a pen in their mouth. Some looked at positive images, like puppies, while grinning, and some did not.

With the first two methods, happiness increased regardless of whether participants were looking at a positive picture, but the results were unclear with the pen-in-mouth method. Overall, however, the study made it clear that faking a grin makes people report being happier.

The idea that facial expressions can influence emotions is known as the facial feedback hypothesis. This isn't true only with smiling; scowling, for example, can make people feel angrier, as Coles' meta-analysis found. Other bodily experiences, like clenching muscles, could make someone feel more tense through a similar type of so-called sensorimotor feedback.

But exactly how this plays out in the brain is unclear. Some experts think posing an expression like a smile triggers a specific happiness-related neural pathway that "creates a full-blown bodily response," Coles said, and the brain interprets this response as happiness. But this idea is highly controversial, he added. Others suggest that the brain simply interprets the smile as a clue that you're happy. Additional theories include that facial feedback impacts how you process other emotional information or makes people think of memories associated with a particular expression and emotion, according to a 2022 study in the Journal of Personality and Social Psychology.

Unfortunately, experts aren't sure whether the results carry over from the lab to the real world, because in real life, there are a lot more inputs to your brain than there are in the lab. If your face is telling your brain that you're happy but everything else is telling it that you're not, smiling might not move the needle on your emotions, Cross said. However, she added, "I definitely don't think it would hurt to smile a few times over the course of the day to see if it affects your mood."