It’s daylight science time again

Why does your breath smell so bad when you wake up? - S.B. and A.B.
This one ought to get you to brush before you go to bed. That smell is ... bacteria gas. Gross, but accurate. There are lots of bacteria in our mouth all the time, feeding on the tiny leftover bits of what we’ve eaten. Ever hear of plaque, the stuff all those toothpaste ads promise to get rid of? Plaque is nothing more than organized colonies of bacteria chowing down on food bits on your teeth.

When we’re awake, some plaque is removed when we chew, talk, drink, even when we breathe. But overnight, when those disturbances in the mouth stop, it’s party time for the bacterial colonies on your teeth, and they multiply like crazy. Their waste products are acids, which cause cavities, and gases, which cause that rude blast of morning breath.

Why do we snore? - S.D.
To bug the person sleeping next to us, of course.

Actually, there are several causes of snoring. All of them have something to do with restriction of the upper airway.

• Kids with swollen tonsils or adenoid glands snore.
• People sleeping on their back snore because the tissues in the neck are pressing down on the windpipe.
• Overweight people snore for pretty much the same reason, or because some of their fat is stored in tissues in the neck.

• INTERACTIVE The biology behind those sleep sounds — and strategies for silencing them

  People with colds snore because they have swollen sinus tissues in their throat.
• Drinking alcohol causes snoring by relaxing the muscles in the throat, which restricts the size of the airway.
• We snore more as we age because of the loss of elasticity in neck tissues, which sag in on the windpipe.
• People with misshapen jaws, larger-than-normal tongues, or on relaxant medications, all are more prone to snore.

So if you try to sleep next to an overweight elderly drunk with a misshapen jaw and a cold who’s taking muscle relaxants ... bring industrial-strength earplugs.

Why is yawning contagious? - P.H.
If you don’t think YAWNING is contagious, see if you YAWN by the time you’re done reading this explanation of YAWNING.

First, let’s dispel a myth. You don’t yawn to take in extra oxygen. “That’s been rejected in lab tests,” says YAWN expert Robert Provine, professor of psychology at the University of Maryland’s Baltimore County campus. He had test subjects breathe air with extra oxygen. For others, he reduced the oxygen intake by giving them air high in carbon dioxide. Neither caused more or less YAWNING.

(YAWN. YAWN. YAWN.)

Provine says “we YAWN when we’re changing states of activity. Going from sleep to wakefulness, like YAWNING in the morning. Or wakefulness to sleep.” (He says we YAWN more in the morning when we wake up, by the way.)

“Concert pianists will YAWN before going out to an important performance. Olympic athletes YAWN before the big event. Embryos begin YAWNING eleven weeks after conception,” Provine notes. He says YAWNING is somehow connected to changing levels of body activity, changes from one state to another, like inactive to active or vice versa, but nobody understands just what the connection is.

“It probably helps stir up the blood and brain chemistry to facilitate those transitions from one level of activity to another.”

Why? “YAWNING is ancient and autonomic,” Provine says. “Maybe it’s to get everyone in the tribe to synchronize their states of activity, to increase the success of the tribe if everyone’s working together. We really don’t know.”

(YAWN. YAWN. YAWN.)

YAWNING is highly contagious, he says. Every vertebrate species YAWNS. Fish YAWN. Birds YAWN. Alligators YAWN. But Provine says it’s apparently only contagious in humans.

Provine has made test subjects YAWN by showing them a YAWNING face. Interestingly, if he shows them just the YAWNING mouth, it doesn’t trigger the YAWNING. If he covers the mouth, and shows them just the nose and eyes of the YAWNING face, it does. He’s made subjects YAWN by talking about YAWNING, or asking the test subjects to think about YAWNING, or by having them read about YAWNING.

Yawning yet?

David Ropeik is a longtime science journalist and currently serves at Director of Risk Communication at the Harvard Center for Risk Analysis. This article is adapted from the archives of “How and Why,” Ropeik’s column about scientific puzzlers, and was first published in March 2000. It has been adapted by MSNBC.com for changing circumstances.

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