There are many reasons for occasional blood in sputum, mainly including the following: 1. rupture and bleeding of the mucous membrane of the nasal cavity, which flows back to the throat and mixes with sputum to cough up, such as dry nasal cavity, deviated nasal septum, rhinitis, sinusitis, etc., which can lead to rupture and bleeding of the mucous membrane of the nasal cavity. 2. bleeding of the gums mixed with sputum, which can also show symptoms of occasional blood in sputum, such as gingivitis, periodontal disease, pulpitis, etc. 3. mucous membrane of the throat Rupture and bleeding, such as acute pharyngitis, acute laryngitis, dryness of the throat and other factors, can lead to mucous membrane rupture and capillary bleeding in the throat. 4, tracheal and bronchial bleeding, that is, bleeding in the lower respiratory tract, includes many diseases, such as acute bronchitis, bronchitis, pneumonia, tuberculosis, bronchial dilatation, lung abscess, bronchopulmonary cancer, etc. Therefore, occasional blood in sputum cannot be ignored and should be clarified as early as possible.