Why is yawning contagious? -Grant, 10, Pullman, WA

Dear Grant,

When I got your question, I met up with my friend Hans Van Dongen, a scientist at Washington State University in Spokane. He works in a research lab where they study sleep. As a cat who appreciates naps, it’s one of my favorite places to visit.

He explained that while yawning is common for lots of animals, we still don’t know why it happens. We do know that once you start a yawn, there’s no stopping it. And as you’ve observed, yawns can be quite contagious.

If someone yawns, people who see the yawn may soon start yawning, too. Some scientists think that the contagiousness of yawns might actually be a way for humans to communicate.

Van Dongen said a lot of people used to think that yawning was a sign of boredom. But after a while, they weren’t so sure about that theory. If you are watching a movie or listening to a long lecture, you might start to yawn, but it might not mean you’re bored.

When you stretch your jaw, breathe in, and let out a yawn, it might be that you’ve slowed down long enough to realize an important fact: You might need to be getting some more sleep.

If a friend catches the yawn, they just might be saying, I could probably use some more sleep, too.

“And this is not an insignificant issue,” Van Dongen said. “Because we mask our sleepiness by being busy all day.”

People generally have a lot of work to get done, so they have to keep busy. Working together in a group was especially important for human survival a long time ago.

While people don’t rely on one another for survival as much these days, yawning still may be a way to communicate among the whole group that everyone needs sleep to be successful.

“Really the only theory that gets circulated much at the moment is that it is a social signal to say, ‘You know what—we should maybe all time out and sleep a little bit more’,” Van Dongen said. “Maybe take a nap or make plans to go to bed earlier tonight.”

After all, the survival of the group often depends on the survival of an individual person. So, it’s important to make sure that the individual people aren’t tired, cranky, or distracted.

“And if yawning is alerting us to that and we are ignoring it because we don’t think much of it, maybe we are losing a lot of money and lives because of drowsiness that could have been avoided,” Van Dongen said.

Catching a yawn could help humans let each other know they should be catching some more Z’s. But maybe there’s more to the story, too. Perhaps you could be a scientist and help us get to the bottom of it.

Sincerely,

Dr. Universe

Got a science question? E-mail Dr. Wendy Sue Universe at Dr.Universe@wsu.edu. Ask Dr. Universe is a science-education project from Washington State University.