Is it true that we yawn when our brains are deprived of oxygen?

Most of us can feel a yawn coming on. The muscles in our jaw begin to tighten, our nostrils might flare, and our eyes might tear up as our mouths stretch open and we inhale a gust of air.

Yawning, a complex reflex, can happen spontaneously, or it can be contagious — when we see, hear or sometimes even think about it, we usually yawn. (Have you yawned yet while reading this?)

The notion that we yawn because our brains need more oxygen, however, is a myth, experts said. A study in the 1980s reported that breathing pure oxygen or gases high in carbon dioxide does not have a significant effect on yawning.

Yawning is a little understood human behavior. “The brain is still a black box,” said Mark Andrews, chair of physiology at Duquesne University’s College of Osteopathic Medicine.

But researchers have theories about yawning.

Yawning may signal changes in state of being

Yawning appears to occur when people are in a state of transition, particularly sleep-wake transitions — when they wake up or when they are drowsy and ready to sleep. They may yawn when they become bored or are experiencing mild psychological distress such as anxiety.

“However, yawning also occurs with high frequency during periods in which people are very excited or there’s a great deal of anticipation,” said Andrew Gallup, teaching professor of behavioral biology at Johns Hopkins University. There are anecdotal reports that Olympic athletes tend to yawn before competition, paratroopers before a first jump and musicians before a performance, he said.

Yawning may help stimulate the brain

Yawning is associated with increased arousal, alertness and wakefulness. It may help the brain wake up or stay awake during tedious activities.

One theory is that by moving the muscles in the face and neck, yawning stimulates the carotid arteries in the neck, increasing blood flow to the brain and waking it up.

Additionally, a 2012 study reported that heart rate, lung volume and eye muscle tension increase during or immediately after a yawn.

“It’s part of the stretching of the muscles,” Andrews said. “It starts with the yawn, but there are connections with other muscular activities, so it gets you up and gets you moving.”

Yawning may help cool down the brain

When temperatures in the brain rise above its baseline — because of increases in mental processing while focusing on a task, exercising or being anxious or excited, for instance — the brain initiates cooling mechanisms including yawning, said Gallup, who has studied the theory.

Some researchers believe this thermoregulation occurs in two ways. First, yawning increases blood flow to the brain and enhances blood flow back to the heart. Second, the deep inhalation of air during a yawn is thought to cool blood in vessels in the nose and mouth. These two processes together replace overheated blood with cooler blood, one study suggested.

There is no consensus, however, on what causes spontaneous yawning or what it accomplishes.

What else you should know

Don’t suppress yawns, experts said. Yawning may serve an important physiological purpose, researchers believe. But because there can be a social stigma around yawning, some people may try to stifle it.

Instead, there are behaviors that may mimic or achieve similar results, Gallup said:

• Chewing gum may reduce yawning by increasing blood flow to the brain, research suggests.

Breathing through the nose may prevent the need to yawn by helping to regulate brain temperature.

Applying a cold compress to the forehead may have a similar effect.

The bottom line: While there is no consensus among experts on what exactly causes yawning or what it accomplishes, yawning is not related to oxygen deprivation.