If the patient appears lower lip black: 1, first of all, we should consider the poisoning type of disease, such as food, poisonous drug poisoning, in food poisoning is often nitrite poisoning leads to black lips, at this time because of a serious lack of oxygen in the body caused by; 2, for the cardiac disease, such as coronary heart disease, unstable angina pectoris, myocarditis, cardiac valvular disease, hypertrophic obstructive cardiomyopathy, these cases will also lead to insufficient oxygen supply capacity of the heart muscle, causing black lips; 3, for the respiratory system of chronic diseases, such as chronic bronchitis, chronic bronchial expansion, chronic obstructive pulmonary disease, pulmonary hypertension, these cases will also be Will lead to insufficient myocardial oxygen supply capacity, causing the lips black; 3, for the respiratory system of chronic diseases, such as chronic bronchitis, chronic bronchodilatation, chronic obstructive pulmonary disease, pulmonary hypertension, these conditions will also know lead to a decrease in oxygen saturation, partial pressure of oxygen is too low, the partial pressure of carbon dioxide is too high, causing the patient to appear anoxic, resulting in the lower lip black.