Good Question

Good Question: Why Do We Yawn?

SACRAMENTO (CBS13) ― A couple of viewers, Denise Voll and Kimberly from Rancho Cordova, want to know if we've finally figured out what causes yawns yet.

That's tonight's Good Question.

You've probably heard the theory that you yawn when your body needs more oxygen. Unfortunately, Dr. Kraig Katzenmeyer says studies don't back it up.

Another idea involves something called surfactant.

"Surfactant is a fine liquid that coats the inside of the lungs that keeps them able to move," says Dr. Katzenmeyer. "There's also a theory that if you don't take a deep breath once in a while that surfactant doesn't spread throughout the whole volume of the lung, so triggering a yawn will cause that surfactant to be spread to areas that maybe weren't used as much when taking shallow breaths."

The problem with that is we yawn so much when we're tired. What would that have to do with our lungs?

"Maybe if you're tired you're yawning more shallowly," says Dr. Katzenmeyer.

A lot of maybes, but one thing about yawning Dr. Katzenmeyer does know for sure…

"Yawning is definitely contagious," he says. "I wish I could tell you why!"

"We don't really know how truly complex the human body is."

So the idea that we yawn to get more oxygen was disproved because studies show when you increase or decrease the amount of carbon dioxide in a test subject, it doesn't affect how much you yawn.

By the way: Research shows that 11-week-old fetuses yawn.

More interesting yawning facts:

• The average yawn lasts about six seconds.
• Your heart rate can rise as much as 30 percent during a yawn.
• 55 percent of people will yawn within five minutes of seeing someone else yawn.
• Blind people yawn more after hearing an audio tape of people yawning.
• Reading about yawning will make you yawn.
• Olympic athletes often yawn before competition.

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