If a patient presents with a sudden darkening and blackening of the lips. First of all, the factors of poisoning should be considered, for example, the patient has acute food poisoning, acute drug poisoning, chemical poisoning, and in these cases, there will be clinical symptoms and manifestations of sudden blackening and bluing of the lips, especially in the case of nitrite poisoning. In addition, if the patient has cardiogenic diseases, such as coronary heart disease or acute or malignant arrhythmia, acute coronary syndrome, acute myocarditis, acute heart failure, it will lead to ischemia and lack of oxygen in the myocardial cells, at which time the coronary arteries will become ischemic, narrow and spasm, because of insufficient blood supply to the heart, which will also lead to sudden blackening of the lips. Finally, if the patient suffers from acute pulmonary decompensation due to various factors, which triggers respiratory failure, he or she will also have the above clinical symptoms and manifestations.