Let's start watching what yawning, really is. According to the dictionary, yawning is the "frenetic opening of the mouth because of lethargy or fatigue". Yawning is a reflex that originates in the brain stem. A yawn usually begins with a feeling in your mouth. Once it happens, it is almost impossible to avoid: your muscles tighten, your mouth opens and lungs suck air inside. With a full yawn, you close your eyes and you stretch out. Some people get watery eyes from yawning: This is because while yawning, the facial muscles are pressing on the tear duct.
Also during yawning some changes occur in your body: your heart rate goes up (up to 30% more), your blood pressure rises and your small blood vessels constrict.
But why do we do it now?
There is still no agreement why people yawn. There are some theories:
- People yawn to rise the oxygen level in the blood. This theory assumes that people yawn to increase the oxygen level in the blood and decrease the carbon dioxide content. Yawning would then be a reflex as a result of a high carbon dioxide content in the air. Because everyone in one room breaths the same air, the same reflex will work on several people. That's the reason that it gives you the impression that yawning is contagious, when in fact it's the simultaneous occurrence of the same reflex. This could also explain why people yawn when they are tired or bored. When people are tired or weary, they will automatically breath slowly. Less oxygen reaches the lungs and decreases the oxygen content of the blood. Also, the carbon dioxide content rises. The reflex is now put in motion and you have to yawn. Because many people are tired around the same time, people will therefore yawn at about the same time.
- Yawning in preparation for exercise. This theory says you're yawning to prepare for your effort.You should therefore only yawn when you have to stay awake. This theory is supported by the fact that a yawn increases heart rate, the blood pressure rises and by yawning you stretch and tighten your muscles.
Unfortunately, none of these theories are supported by science and it remains a mystery why we yawn.