KnowHow team explains: Yawn — the open-mouthed, face-stretching gesture that commonly tells others, I’m tired. But there is more to why we yawn than signalling that we’re tired and need sleep. We yawn because we need extra oxygen; our body senses we’re running low on oxygen, and forces us to take an extra big gulp of air.

Yawning is healthy for our lungs. Perhaps, every now and then, we get pockets and wrinkles in our lungs. A deep breath and a good stretch will smooth these wrinkles out. We know that yawning is very common among creatures with a backbone, including fish, crocodiles and humans. All these creatures have a special fluid in their lungs, and yawning might spread this fluid out.

Yawning is also a form of social communication. We yawn when we’re tired or breathe less, resulting in increased amounts of carbon dioxide and decreased amounts of oxygen in our systems. Yawning, therefore, serves as a way to gather more oxygen into the system.

It has often been observed that the act of yawning is contagious. Mass display of tiredness, mental fatigue and boredom is often triggered by the first act of someone yawning, especially during seminars or lectures. Someone’s yawn in such an environment often signal to others’ subconscious that it has been a long time since they have been passive.

The question was sent by

Sunil Shashtri via email