Coughing up gray sputum, the common causes are: environmental factors, long-term smoking, respiratory diseases, etc.. 1. Environmental factors: usually related to the nature of the occupation, such as miners, dust operators, long time in the charcoal, iron or dust in the working environment, the bronchial mucosa will secrete mucus will be adhered to the dust, stimulate the body to produce a cough, and then can cough up gray sputum. 2. Long-term smoking: Harmful substances in smoke will stimulate the bronchial mucosa and glands, resulting in increased secretion, leading to coughing and phlegm. The nicotine and nicotine in tobacco will be adsorbed on the phlegm, causing the color of phlegm to turn gray. 3. Respiratory diseases: for example, common chronic pharyngitis, respiratory tract infections, as well as schistosomiasis, pulmonary amoebiasis or other atypical pathogenic bacteria infections, can appear to cough up gray sputum, it is recommended to go to the respiratory department for a clear diagnosis in a timely manner, and comply with the doctor’s instructions for treatment. To sum up, the phenomenon of coughing up gray sputum, it is recommended to clarify the cause of the disease and timely treatment. If you work in a polluted environment, you need to do a good job of protection.