Usually, colds are caused by viral infections and can appear as a clear runny nose. The appearance of blood inside the nasal mucus may be due to the rupture of capillaries in the nasal cavity, dry rhinitis, nasal tumors and other reasons. 1. Rupture of capillaries in the nasal cavity: it may be the inflammation caused by viral infection, which may result in congestion and edema of the nasal mucosa, as well as symptoms such as runny nose. When you blow your nose with more force, the rupture of capillaries in the nasal cavity will lead to bleeding, which will result in blood in the nasal mucus. 2. Dry rhinitis: it may be that the patient himself suffers from dry rhinitis, which is related to staying in a dry and dusty environment for a long time, which can easily cause the dryness of nasal mucosa and induce the patient to pick his nose, and then a small amount of nosebleed occurs, which can also cause the symptom of blood in the nasal mucus. 3. Nasal tumor: it may also be the nasal cavity, sinus papilloma and other nasal tumors, the appearance of intranasal mass, often accompanied by intranasal reddish new organisms or easy to bleed polypoid material, which causes runny nose, nosebleed or the phenomenon of blood in the nasal mucus. In addition, the cold snot with blood inside can also be seen in other diseases, it is recommended that patients seek medical attention in a timely manner to avoid delay.