The most common cause of bloody nasal mucus is inflammation of the upper respiratory tract caused by colds, which leads to congestion of the nasal mucosa and the development of catarrhal symptoms, resulting in the phenomenon of blood in the nasal mucus when running or blowing the nose. In addition, blood in the nasal mucosa can also occur when the nose is runny or when the nose is blown. Blood in sputum is relatively more complicated and may be caused by hemoptysis. More common causes are pneumonia, bronchiectasis, or even lung cancer. Patients with symptoms of blood in sputum need to go to the hospital for further examination to find out if there is any underlying disease in the lungs.