Elderly people using their mouths to breathe out can be caused by physiological reasons, but also by disease. 1. Physiological reasons (1) Habit: Some old people like to breathe through their mouths when they are young and do not have the habit of breathing through their noses, so they are used to breathing through their mouths when they are old. If this is the case, it is a normal phenomenon and there is no need to worry too much. 2. Disease causes: If the old man did not have the habit of breathing through his mouth before, it may be caused by disease. (1) Nasal disease: due to nasal trauma or other disease-causing factors that lead to nasal disease, there is a lack of ventilation in the nose, the elderly will breathe through their mouths. At this time, you need to go to the hospital in time, to clarify the cause of the disease, symptomatic treatment. (2) respiratory diseases: such as acute and chronic bronchitis, emphysema, chronic obstructive pulmonary disease, pulmonary fibrosis or asthma and other respiratory diseases may lead to hypoxia, there is a lack of oxygen supply, the old man will use his mouth to breathe. At this time, it is necessary to promptly treat the primary disease. Elderly people need to pay attention to the mouth out of breath, if accompanied by dyspnea, need to go to the hospital in time to receive the cause of the treatment.