From a baby to an adult, and even animals, yawning is one of those things that most of us do multiple times a day, especially if we feel tired or bored. Fun fact: I have yawned at least three times while writing this—it is that contagious! However, did you ever wonder why yawning seems to occur more often when we are tired? While it is a completely natural and ubiquitous behaviour, the science behind why we yawn more when tired is intriguing and quite complex.

Yawning is very often associated with sleepiness since it normally occurs between waking up and drowsiness. The cause of yawning itself has not been defined yet, but some prevailing theories relate it to fatigue.

• Cooling the Brain

One of the popular theories is that yawning cools down the brain. Just like our body sweats to regulate temperature, a yawn may be some sort of mechanism of cooling the brain when it becomes sluggish, especially due to tiredness. When a person is fatigued, all body functions, which also include brain activity, gradually come to a slowdown, which could lead to an increase in yawning. Through yawning, we increase airflow into the mouth, thereby achieving a lower temperature of the brain and improved functioning of its part.

• Oxygen and Carbon Dioxide Regulation

Another theory is that yawning allows us to take in more oxygen and to expel more carbon dioxide. Perhaps fatigue alters breathing, making it shallow and incomplete, and yawning becomes a mechanism for increasing oxygen supply to increase alertness. The additional oxygen might improve the short-term wakefulness produced by yawning, even if temporarily.

• Social and Psychological Factors

Yawning also can be contagious. When you see someone else yawning, you may feel a natural urge to do so too. Such behaviour is connected with social bonding and empathy. Probably this is why yawning seems more frequent in social environments, especially when people are tired or bored together.

A tired brain is an inefficient one, and its energy levels go down. Thus, the body might resort to yawning as a weapon against fatigue. So, although it can be a very natural response, it also proves that the body needs rest. Getting proper sleep helps reduce yawning because fatigue is the most common cause of this reflex.

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