The most common factors are acute toxic factors, such as acute food poisoning, especially nitrite poisoning, in which patients will have cyanosis and cyanosis of the skin around the body, with blackening of the lips and mouth as the main clinical symptoms. 2, some cardiogenic factors, such as coronary atherosclerotic heart disease, myocarditis, pericarditis, endocarditis, or other factors that lead to insufficient blood supply and oxygen supply to the heart. 3, some respiratory diseases, such as chronic bronchial dilatation, chronic obstructive pulmonary disease, chronic pulmonary heart disease, pulmonary hypertension, when the body will have low partial pressure of oxygen, arterial blood oxygen saturation, resulting in lack of oxygen and cause the black lips.