If you travel anywhere in the United States and ask someone to take your picture for you, there’s one thing you can be sure they’ll ask you to do: Smile!

Here in the U.S., we love a good smile. On TV, in ads and in day-to-day interactions, a big, bright smile full of straight, white teeth is seen as a sign of friendliness, happiness, confidence and health. If you’re not smiling, there’s a good chance someone will ask you what’s wrong.

But this isn’t the case within every culture. In fact, in some parts of the world, a smile might be met with suspicion or concern ― or even viewed as a sign that maybe you’re not so bright.

This isn’t the case in many parts of the world, however. For instance, the study noted that famously stoic Russia has a well-known saying about smiles: “Smiling with no reason is a sign of stupidity.” Guidebooks for visiting Norway and Poland helpfully point out that smiling at a stranger on the street there might be taken as sign of insanity. And in other parts of the world, such as some Eastern and Middle Eastern countries, a smile can also send mixed signals.

There are several possible reasons why certain cultures are attracted to smiling faces while others are less so.

What a smile means and how it’s perceived may have a lot to do with how diverse a country’s population is. Multicultural countries with high levels of recent immigration, such as the United States, Canada and Australia, are more likely to view smiling faces favorably, according to a study that surveyed 5,000 people in 32 countries.

Why? In societies where people who spoke many languages had to live and work together, non-verbal communication, such as smiles, were an effective way to overcome language barriers and form communities. A smile could indicate that a person was friendly, and might be willing to cooperate and share resources, rather than compete for them.

Meanwhile more homogenous cultures, such as Japan, had a predominant language, a stable population and an established social hierarchy. This meant non-verbal communication was more nuanced. Here, smiling was often less a friendly gesture than a subtle display of status. It might be used by someone in a position of power to indicate that it’s OK for a person to speak ― or that the person should stop talking.

Does corruption corrupt smiling? Yes. When presented with the same smiling images, people from countries with high levels of corruption and bribes perceived the people pictured to be less trustworthy than did people from countries with less corruption.

A smile is a smile, right? Wrong. Along with whether you smile, different cultures also judge how you smile.

In the United States, for instance, when you smile, you go all in. That means big and broad, letting everyone see those glorious teeth. But in other parts of the world, a big, toothy grin is considered at best gauche, and at worst, gross.

For instance, the Chinese tend to favor a more tight-lipped approach. In fact, a study that reviewed photos of U.S. and Chinese leaders found that the latter consistently favored a more neutral smile while the U.S. officials preferred to look “excited.”

Certainly, regardless of culture, most of us would agree that having a mouth full of healthy teeth is a good thing. Just remember, though, that when you travel abroad, not everyone wants to see them.

Before you visit another country, don’t forget to research social etiquette and norms. That way, you’ll make sure your smile is saying what you think it is.