The lips are the visible mucous membrane part of the body, and its color reflects the oxygen content in the blood. If the lips are always blue-purple and black, consider the low oxygen content in the blood. Possible diseases include long-term chronic lung disease or acute pulmonary artery tethering, where a clot in the pulmonary artery causes obstruction of pulmonary ventilatory function, resulting in a drop in blood oxygen and purple lips. Some patients may also have congenital heart disease, congenital heart disease atrial defect or ventricular defect, there are left and right shunts in the heart, also affect the blood in the lungs to occur oxygenation, low oxygen resulting in purple lips, serious patients can appear the circumference of cyanosis.