Purple lips need to be alert to obstructive pulmonary emphysema, cyanosis congenital heart disease, methemoglobinemia and other causes, the patient should pay attention to timely diagnosis to find out the cause of the disease. 1. Obstructive pulmonary emphysema: after the occurrence of obstructive pulmonary emphysema, the lung ventilation, ventilation function will be impaired, resulting in patients with low ventilation function, resulting in poor respiration leading to hypoxia and thus the symptoms of purple lips. 2. Cyanosis type congenital heart disease: its mechanism is due to part of the venous blood is not oxygenated through the lungs, through the abnormal channel into the arterial blood circulation, resulting in shunt flow more than 1/3 of the cardiac blood volume can cause cyanosis. The main manifestation is purple lips and the whole body. 3. Methemoglobinemia: when the content of methemoglobin in the blood is too high, the hemoglobin will lose the normal oxygen-carrying capacity, which will lead to cyanosis of the skin mucosa and lips. The causes of purple lips are many, if the patient after the occurrence of purple lips should immediately go to the hospital for examination to clarify the specific causes.