Q. Is there a purpose to a yawn? I know it means you’re sleepy, but is the body trying to accomplish something by the act of yawning?

A. People yawn when they’re tired, but also when they wake from a night’s sleep. We yawn when we’re bored, but also when we’re anxious, or hungry, or about to start a new activity. Yawning is contagious — we often start yawning the minute someone near us starts.

“There are so many triggers. People who sky-dive say they tend to yawn before jumping. Police officers say they yawn before they enter a difficult situation,” said Adrian Guggisberg, a professor of clinical neuroscience at the University of Geneva.

Reading about yawning makes people yawn. You are probably yawning right now.

But the physiological purpose of a yawn remains a mystery. “The real answer so far is we don’t really know why we yawn,” Dr. Guggisberg said. “No physiological effect of yawning has been observed so far, and that’s why we speculate. It’s possible yawning doesn’t really have a physiological effect.”