Clear nasal mucus with blood may be caused by acute rhinitis, allergic rhinitis, nasal septum deviation. 1. Acute rhinitis: due to the stimulation of the nasal mucosa caused by viruses, resulting in local congestion and swelling, and increased secretion, resulting in the phenomenon of runny nose, with the increase in the brittleness of the nasal mucosa, which can easily lead to nosebleeds. 2. Allergic rhinitis: patients in contact with allergens, such as pollen, animal dander, etc., leading to nasal mucosa metamorphosis, resulting in runny nose, paroxysmal sneezing and other symptoms, when the nose itchy, runny nose, often rubbing the nose, it is easy to lead to rupture of the nasal mucosa, causing bleeding. 3. Nasal septum deviation: some cases will have a small amount of runny nose and blood in the runny nose, especially after the temperature change stimulation is more likely to attack. The blood in clear nasal discharge should go to the hospital in time, and the doctor will find out the reason and then take the treatment accordingly.