Researchers say the key to making new friends is all in the mouth. Show your shiny whites, and friendships are easier to come by.

The reason smiling is key to new and healthy relationships is that people are more attune to positive emotions when they're forming new relationships.

In a new study on emotional cues and relationship formation, researchers were able to show the importance of positive emotions (like smiling) via two experiments.

One experiment showed that couples were able to accurately track each other's positive emotions. The other showed that people watching a movie with a stranger were more likely to feel a kinship toward him or her if the stranger expressed positive emotions.

"Our findings provide new evidence of the significance of positive emotions in social settings and highlight the role that positive emotions display in the development of new social connections," study leader Belinda Campos, a researcher at the University of California, Irvine, said in a press release. "People are highly attuned to the positive emotions of others and can be more attuned to others' positive emotions than negative emotions."

Campos says the experiments also showed that people are very good at recognizing a sincere smile versus a fake smile.

The research was published in the journal Motivation and Emotion.