There are many mysteries in medicine, but one human and animal behavior that has been observed for years but is poorly understood, is yawning. It is easy to define since it is so common. It is a form of reflex that involves a deep inspiration, opening the jaw wide, and a rapid exhalation of the inspired air. There is generally a feeling of relaxation immediately after the yawn.
Why do we yawn?
Answering this question is not nearly as easy as defining the action. There are a number of theories about why we yawn, but remarkably little good research on this topic. There are several agreed upon causes for yawning, however.
First, when changing elevation rapidly as in an airplane, you will both voluntarily (on purpose) yawn and also involuntarily (not on purpose) yawn to try and equalize pressures within your ear. This works and is an accepted reason for yawning.
Another indisputable cause of yawning is called social empathy. What this means in plain English is “suggestion.” If you see someone yawn, or if you read about yawning (like right now reading this column) some people will yawn. In fact psychologists have proven that the more empathetic you are, the more likely you are to yawn when someone else does. There has been fascinating research about the hierarchy of this suggestion. If you are very close to a person emotionally, you will yawn if they do. The rank order of this suggestion is family, friend, stranger. The closer one is to the person who yawns, the more likely one is to yawn as well.
Yawing clearly is associated with sleepiness and boredom. However, almost paradoxically, it is theorized that yawning is not a sign of sleepiness or boredom, but actually a reflex that your brain induces to wake you up or make you more alert.
Yawning is associated with some hormones that are released that briefly increase the heart rate and alertness. So actually the reason that one yawns when tired or bored is the body’s attempt to keep you alert and awake — if only for a brief time. I suppose this is an evolutionary response related to a time where if one were asleep or inattentive something bad might happen to you!
Related to arousal is the common phenomenon of yawning upon awakening after sleep or nap. This is further evidence that yawing is a stimulation and arousal reflex rather than the opposite.
A final theory on the cause of yawning is that it is a reflex that helps cool a warm brain. This is unproven and although there are some examples of yawning in heat related scenarios, yawing is not something we see when playing sports or playing in the sun. Physiologically, deep breaths and open mouths can cool the brain slightly, but the evidence that this is a real cause of yawning is not convincing.
A logical but disproved theory on why we yawn is to improve oxygen in the blood or remove carbon dioxide. This seems logical since yawning does bring in more oxygen with a deep breath and the expiration removes more carbon dioxide than the usual breath, but research by putting people in low-oxygen or high- carbon-dioxide environments does not cause yawning.
Can yawning be a symptom of disease?
The short answer is that yawning is normal. It is common and usually is totally benign. However, if there is an increase in yawning that cannot be explained by lack of sleep or some of the other causes mentioned above, then yawning can be a symptom of some disease.
The most common medical problems that are associated with increased yawning are sleep deprivation, insomnia, sleep apnea, narcolepsy, and many medicines that cause sleepiness. There are some other medical diseases that cause yawning including bleeding around the heart, brain tumor, multiple sclerosis, stroke, and even heart attack.
The bottom line
In most people yawning is a normal reflex, although poorly understood. However, if you experience excessive yawning for no apparent reason, it is wise to visit your physician and make sure there is nothing going on that is abnormal.