A yawn lasts about 6 seconds, during which people close their eyes and relax their nerves and muscles completely. Therefore, it can be considered that yawning makes people get the best rest physically and psychologically and has an important physiological protection effect on the human body. Some people think that yawning is a manifestation of brain hypoxia. By yawning and taking a deep breath, the human body increases oxygen in the blood and discharges more carbon dioxide, thus making people more energetic. When people are sleepy, they often yawn constantly to remind people that their brains are tired and need sleep and rest, so yawning is also a hypnotic method. People often yawn repeatedly when they are about to enter a stressful job. This may be because the human body increases more oxygen in the blood through deep inhalation and improves the activity ability of the brain.

In a word, yawning is an instinctive reaction of human body, just like heartbeat and breathing, which is not controlled by human will. It has a good protective effect on protecting brain cells, increasing oxygen supply to brain cells and improving human stress ability.