Cough with black mucus can be caused by respiratory bleeding, gastrointestinal bleeding, inhalation of black substances and other factors. 1. Respiratory bleeding: tuberculosis, bronchial dilatation and other respiratory diseases can lead to respiratory bleeding, blood in the respiratory tract after too long a period of time can be oxidized and become black, coughing with sputum can be manifested as black mud. 2. Upper gastrointestinal bleeding: gastroduodenal ulcer, rupture of esophagogastric fundic varices, esophageal cardia mucous membrane tear and other diseases can appear upper gastrointestinal bleeding performance, blood can be black, brown, etc., the bleeding is large, easy to trigger shock. 3. Inhalation of black substances: living in areas of serious air pollution, or long-term work in the carbon foam, dusty environment, may be inhaled for a long time too much black substances, and sticky adherence to the respiratory tract, when coughing with the sputum discharge can be manifested as black mud. When coughing with black mucus, you should consult a doctor in time, under the guidance of a specialist to actively carry out appropriate treatment, which will help to relieve the discomfort symptoms as soon as possible.