Black lips is a manifestation of cyanosis, cyanosis refers to the blood contains excessive reduction of hemoglobin, resulting in the appearance of cyanosis of the skin and mucous membranes, and the whole body mucous membranes can appear in the above manifestations, but the lips, tongue, oral mucous membrane, tip of the nose, cheeks, earlobes and other parts of the skin is the most obvious. Cyanosis can be caused by the following diseases, such as respiratory diseases, cyanosis caused by respiratory insufficiency, such as acute and chronic respiratory diseases, pulmonary vascular diseases, pulmonary arteriosclerosis, primary pulmonary hypertension and so on, and it can be seen in the case of pulmonary stasis. Heart diseases, such as congenital heart disease, tetralogy of Fallot, tricuspid atresia and so on, can also lead to the appearance of cyanosis.