Why do we yawn?

Although it is mostly an involuntary action, yawning may not be something that’s given too much thought.

To understand the function, Dr. Harriet Davis, a family medicine physician at Novant Health Mint Hill Family Medicine, describes yawning as “an involuntary reflex where the mouth opens widely with a powerful widening of jaw, together with a long and deep inhalation through the mouth and nose, followed by a slow expiration, associated with a feeling of comfort.”

Yawning can be caused by a slew of factors: fatigue, boredom, stress, or empathy. The most commonly known causes are boredom or tiredness, but the truth is, there are a lot more reasons. When you watch someone yawn and you respond in kind, you may make a joke about it’s contagious, but actually is, although no one is entirely sure why yet.

“Yawning is a reflex that does not follow many consistent patterns,” Davis said. “One of the most common theories is that contagious yawning is a sign of empathy for others. Seeing a person yawn may cause the viewer to yawn, especially if they are close to or comfortable with that person.

“The full reason for contagious yawns in humans is unknown and therefore, contagious yawning remains an enigma to scientists.”

Contagion is a phenomenon when it comes to yawning. Chimpanzees and humans are the only species in which it spreads, and simply reading about yawning can sometimes trigger a response, like it may be doing for you right now. Because the contagion is so complex, it’s equally as hard to understand.

As for fatigue, it can be a reason, but there’s a little more to it than that.

“When we are bored or tired, we don't breathe as deeply as we usually do and our bodies take in less oxygen because our breathing has slowed,” Davis said. “Therefore, yawning helps us bring more oxygen into the blood and move more carbon dioxide out of the blood.”

On the flip side, yawning can be a sign of alertness in some cases as well. You may actually be focused and quite aware.

“When a person yawns, the heart rate quickly rises during a yawn,” Davis said. “This increased heart rate suggests yawning can be a sign of alertness rather than sluggishness.”

Although it isn’t quite as common as the action itself, excessive yawning without any obvious cause can be a sign of a medical condition like sleep disorders, epilepsy, migraines, or heart disease. Davis recommends “anyone experiencing excessive yawning with no apparent cause should contact a medical professional as soon as possible.”