Some people like to breathe with their mouths open when they sleep, which is harmful to their health and should be corrected. Tang Sun Simiao said in "Thousands of Women: Daolin Xiuxing": "When you lie down at dusk, you should always close your mouth. When you open it, you will lose your breath. When evil enters your mouth, you will quench your thirst and lose your blood color for a long time. "People are required to close their mouths and breathe through their noses after lying in bed at dusk, and don't open their mouths to breathe, otherwise some diseases will occur. This statement is very scientific. Because there are nose hairs in the nostrils, it can block dust and dirt and filter the inhaled air. If you breathe with your mouth open, not only the dust in the air is easily inhaled into the respiratory tract, but also the airflow flows back and forth in the oropharynx, which will make people thirsty after waking up and even cause many respiratory diseases. Some health care experts regard the danger of lying down and breathing with your mouth open at night as more serious. For example, Shi, a famous health care practitioner in the early Qing Dynasty, said in the book "The Secret of Longevity": "The most important thing is to keep your mouth shut when you sleep at night. When you open your mouth, you will lose your vitality. When evil enters your mouth, blood will produce various diseases. Anyone who sleeps with his mouth open at night will get sick when his teeth are touched by the gas coming in and out, but those who sleep with his mouth open will have early teeth. You can check them. "Shi warned people with his clinical experience that lying at night and opening his mouth not only damages vitality, but also easily leads to blood loss syndrome such as dull complexion, lethargy, dizziness, cold limbs and pulse deficiency, and also causes unstable teeth and premature loss, which should be highly valued by people. But some people are forced to open their mouths to breathe because of nasal polyps or rhinitis. If this happens, you should go to the hospital for examination and treatment in time.