If a patient develops black lips and mouth, the specific causes are as follows: firstly, it should be considered whether it is caused by the factors of poisoning, for example, nitrite poisoning in food poisoning can lead to cyanosis of the patient’s lips accompanied by blackness. Secondly, if the patient is in a state of long-term lack of oxygen, the black lips will also appear, for example, if the patient has chronic bronchitis, bronchial dilatation, chronic obstructive pulmonary emphysema, chronic pulmonary heart disease, pulmonary hypertension, and is in a state of long-term lack of oxygen, the lips will also appear black. Then, for chronic heart diseases, such as chronic myocarditis, pericarditis, dilated heart disease, chronic heart failure, patients will also have black lips due to insufficient blood supply to the heart.