There are many reasons for yawning, and the common causes are mainly the following: 1, physiological factors, such as overwork, lack of sleep, staying up late, etc., can cause physical fatigue, mental discomfort, and thus the symptoms of yawning always. 2, cerebral artery blood supply is insufficient, the disease is due to atherosclerosis caused by the decline in the elasticity of blood vessels, blood vessel wall thickening, thus causing the relative narrowing of blood vessels, blood flow is reduced. The brain appears ischemic and hypoxic, through yawning can help intake more oxygen to relieve the symptoms of brain hypoxia. 3, hypoglycemia, low blood sugar when the brain energy intake is not enough, can also cause fatigue, mental fatigue symptoms, easy to appear yawning, immediately after eating can effectively relieve symptoms.