The common reasons for spitting black and yellow phlegm that is sticky are infectious diseases of the respiratory tract, long-term smoking or inhaling other harmful particles, etc. You need to consult a doctor in time to find out the reasons. 1. Infectious diseases of the respiratory tract: Inflammation of the bronchial tubes, inflammation of the lungs and other related diseases can lead to coughing, coughing up black sputum or yellow sputum, sputum thick phenomenon, generally more common with bacterial infections. Viral infections are mostly characterized by white sputum or simply coughing, with no obvious symptoms of coughing up sputum. 2. Long-term smoking: tobacco has a large number of harmful substances, the above harmful particulate matter, by the respiratory tract cilia adsorption, can form a black phlegm thick phlegm is coughed up out of the body. 3. Inhalation of other harmful particulate matter: for example, smoke from burning straw, smoke inhaled at the scene of a fire, hazy weather or air pollution caused by car exhaust, etc., can also lead to coughing up black phlegm phlegm thick phenomenon. In summary, spitting black phlegm is very thick may be seen in a variety of reasons, need to go to the hospital to further clarify the cause of the disease, targeted treatment.