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Unsurprisingly, your face does a lot to communicate how you're feeling. Whether you're happy about seeing your crush or shocked at the plot twist in a TV show, it probably shows.

Unless you're like, a star poker player. What's more surprising is that, according to some research, your facial expressions are also a two-way street. The idea is known as the facial feedback hypothesis, and it says that your expressions can change the emotions you experience.

So if you're having a crummy day, supposedly turning that frown upside-down will make you feel better. It sounds great, but whether or not it's true is up for some debate. Many researchers over the years have tried to find out, and the tale of their work is a great story of science in action.

The idea behind the facial feedback hypothesis is based on one of your senses, called proprioception. It provides information on what your muscles and joints are doing and their positions relative to each other, so you don't need to look to know where, say, your left foot is. According to the facial feedback hypothesis, your facial expressions are just another extension of this.

They're also important information and can make your emotions stronger or weaker, or maybe even cause them. Research into this really started in the 1970s, and it has been a tricky road. Experiment participants were typically asked to make different facial expressions, often by contracting certain muscles, like turning up the corners of their mouths.

Then researchers measured their emotions through their body's reactions to things like electric shocks—really!—or by rating their mood. But the big problem is, we know what emotions go with smiling or frowning. So people might have just been saying they felt happy when they were obviously smiling because… well, that's what you're supposed to do.

Maybe asking people to smile is what mattered, not the actual expression. Then, in 1988, a paper came out in the Journal of Personality and Social Psychology that figured out this problem, and its results have been included in many intro psych textbooks. In a series of two experiments, researchers had 175 university students hold a pen in their mouth while trying to do some simple writing and drawing tasks.

They were told scientists were interested in learning more about what these tasks might be like for people with physical impairments. But the researchers actually wanted to study the participants' emotions. See, holding the pen between their teeth, it made their mouth form a smile.

And between their lips, a sort of pout. But the key was, participants didn't realize their faces were making these expressions, so they couldn't bias any results. Later, when they were asked to rate some comics, subjects tended to report they were funnier if they'd made the smiling face.

And since they didn't know they'd been smiling, it seemed like expression itself really affected things. Of course, in the years since, many scientists also questioned the accuracy of this study. Because welcome to research.

In a 2016 paper, 17 research groups from around the world came together to try to replicate it, each running the study almost exactly like the original and testing close to 1900 participants. Except, they couldn't find the effect. But that didn't necessarily mean the classic study was wrong.

As it turns out, the study and the replication might both be correct. See, a big part of science is that one research study seldom proves or disproves anything. Each just offers evidence that needs to be evaluated and critiqued.

The heart of science is to test things over and over in new ways, revising our ideas as we learn more. The goal of the replication study was to figure out whether having people hold pens in their mouths and rate comics was a good way to test the facial feedback hypothesis. Because they failed to find the same results, it seemed the original study's results might have happened just by chance or some other factor.

Except, they missed a pretty big detail, which one of the original researchers and others pointed out later. In the original 1980s experiment, people weren't watched while they did the tasks. But in the replication, they were recorded by a video camera so researchers could check if they held the pens correctly.

It makes sense to want to check that, but psychology research has also shown that we tend to react differently when we're watched, including in how much we pay attention to what's going on inside our minds. And that likely interrupted the effect. Other researchers specifically tested this in 2018 and found that, with their nearly 200-person sample, this simple difference made a big impact.

When participants had a camera recording them, the facial feedback effect didn't happen. But when there was no camera, it did. This means the original and the replication might both be right.

And it goes to show that we shouldn't always be quick to judge when a new study comes out. But what does this mean for you? Do your facial expressions actually do anything?

Well, probably. Today, lots of research has been done using various techniques, and a lot of it does support the facial feedback hypothesis. This idea is even being used to create some new treatments.

Like, one 2017 study found that unknowingly smiling seemed to stop food cravings in 61 young women, especially those prone to emotional eating. And a few studies over the last decade have found that injecting Botox into frown lines might actually decrease depression symptoms. But before you call your doctor, as always, more research is needed.

For now, the most we can say is that the evidence is promising—and that's okay. Psychology is inherently full of unanswered questions, and sometimes the answers aren't as straightforward as you want them to be. But hey, people are pretty complex, too.

Thanks for watching this episode of SciShow Psych! We love exploring what makes our minds work and how all those things shape who we are and what we do. If you'd like to keep learning with us, you can watch another one of our episodes or go to youtube.com/scishowpsych and subscribe. [OUTRO ♪].