If the patient has a dry and black mouth and nose: firstly, the factors of poisoning should be considered. If food poisoning, drug poisoning or bad gas poisoning is caused by various reasons, there will be cyanosis of the mouth and lips and black color, especially in the case of nitrite poisoning, there will be obvious clinical typical symptoms. Secondly, for some chronic cardiogenic diseases, such as coronary artery disease, unstable angina pectoris, myocarditis and other factors causing chronic cardiac insufficiency, this condition will also have the symptom of blackened lips and mouth. In addition, if the patient has chronic pulmonary insufficiency, such as chronic bronchitis, bronchiectasis, chronic obstructive emphysema, pulmonary heart disease, pulmonary hypertension, it will cause low partial pressure of oxygen and high partial pressure of carbon dioxide, which will also have the clinical manifestation of black lips.