It is not good to breathe through the mouth while sleeping at night. Most people breathe through the nose at night, and breathe through the mouth because there may be problems with the nose while sleeping, resulting in poor ventilation. The most common reasons for breathing through the mouth may include nasal septum deviation, inferior turbinate hypertrophy, or inflammation of the nasal cavity resulting in poor ventilation of the nose. It is easy to have lack of oxygen during night sleep, or even sleep apnea syndrome, and the next day you will feel uncomfortable symptoms such as dry mouth, headache, dizziness, fatigue, irritability, etc. Over time, it may even lead to memory loss and inability to concentrate. There is also incorrect sleep position, can also lead to breathing with the mouth, such as sitting and supine position is also easy to lead to breathing with the mouth, and change to side sleep will make the situation improved.