What causes blushing? Science finally reveals the answer.

Scientists have finally figured out what causes blushing — and they cracked the code by intentionally placing their study volunteers in embarrassing situations.

In an unconventional new study, published July 17 in the journal Proceedings of the Royal Society B, researchers asked 40 teenage girls and young women to sing karaoke while being filmed. The study volunteers sang four notoriously difficult-to-sing tunes: "All I Want for Christmas Is You" by Mariah Carey; "All the Things You Said" by t.A.T.u.; "Hello" by Adele; and "Let It Go" from Disney's "Frozen."

After the recording session, the researchers scanned the volunteers' brains using function magnetic resonance imaging (fMRI), which indirectly measures brain activity by tracking blood flow through the organ. During the fMRI, the participants were shown the recordings of their singing, as well as that of another participant who sang at a comparable level to them. They also watched recordings of a professional singer of a similar age performing the songs.

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To make things potentially more awkward, researchers also told the participants that an audience would watch their own recording with them.

In addition to monitoring the activity of neurons in the participants' brains, the researchers measured how much the temperature of the volunteers' cheeks increased — an indicator of their level of blushing.

The team found the volunteers blushed more when they were watching themselves versus other people singing. And overall, the more a person blushed, the greater the activity of neurons in their cerebellum. The cerebellum is a region of the brain that controls movement and coordination. However, recent research suggests it may also be involved in emotional processing, among other functions. Specifically, the researchers saw high activation in part of the cerebellum called lobule V, which has previously been shown to play a role in emotion.

Another brain region that lit up in participants who blushed while watching themselves was one involved in the early stages of visual processing. The researchers say this implies that blushing is tied not only to emotional processing but also to brain circuits that help direct a person's attention. In other words, blush-inducing videos of a given participant seemed to pique that person's attention more than videos of others, they theorized.

On the flip side, the team didn't find any association between blushing and the activation of so-called high-order brain regions — the parts of the brain that enable us to complete complex cognitive tasks, including making sense of oneself and others.

"Based on this we concluded that thinking about others' thoughts may not be necessary for blushing to occur,'' lead study author Milica Nikolic, an assistant professor in developmental psychopathology at the University of Amsterdam, said in a statement. "Blushing may be a part of the automatic arousal you feel when you are exposed and there is something that is relevant to the self," Nikolic said.

The researchers added in their paper that blushing may be "triggered by a sudden surge of alertness when socially exposed." They argued that it's likely a spontaneous emotional reaction rather than something that arises from higher self-reflection, such as actively thinking about how others perceive you.

The team acknowledged several limitations of the study. For instance, they evaluated blushing only by looking at changes in cheek temperature. Using additional metrics, such as measuring blood flow in the face, could provide more detail about this process.

Going forward, the team wishes to study blushing under different scenarios and in more diverse cohorts. One potential research avenue would be to see whether the same findings can be replicated in younger children who have not yet developed more-complex cognitive skills.

Understanding more about how blushing arises may also shine a light on why some people with anxiety disorders develop a fear of blushing, they said.

"When we understand the mechanisms of blushing, we can target the fear of blushing better as well," Nikolic said.

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