Before answering this question, first we need to understand how phlegm is formed. Phlegm formation comes from several sources: first, it is the mucus secreted by the glands of the mucous membrane of the trachea. Secondly, it is a mixture of necrotic material from infectious substances and white blood cells after they have fought against each other. Thirdly, there is the foreign matter that the body inhales into the airway from the atmosphere, such as dust, dirt, fibrous matter, which mixes with the mucus, and all of which can be expelled from the body in the nature of sputum. Therefore, from the bacterial point of view, clinically speaking, after the necrosis of the infected bacteria, the black state is mainly Bacillus anthracis. But if Bacillus anthracis is infected, its clinical symptoms will be very serious and obvious, which may lead to sepsis and death of the patient. So it depends on the patient, could it be anthrax? It’s generally less likely. In addition, it could be some pollutants in this atmosphere, dust or some fibrous material, smoking patients with inhaled nicotine deposited in the lungs, these things mixed with mucus and coughed out of the body, it becomes such a black material. In addition, if you have a small amount of blood seepage from the capillaries inside the airway, the early time is not timely discharged from the body, in the airway after the accumulation of the formation of stale blood, and mucus after mixing with coughing out, will also show black or coffee-colored sputum.