Sudden nosebleeds can be caused by external causes, rhinitis, nasal polyps and other reasons. 1. External factors: dry weather, insufficient water intake, dry nasal mucosa in the nasal cavity, increased vascular fragility, forceful nose blowing and nose picking will lead to damage to the nasal mucosa, causing sudden nosebleeds. 2. Rhinitis: prolonged inflammation of the patient’s nasal mucosa can easily lead to erosion and ulceration of the nasal mucosa, which can lead to sudden nosebleeds. 3. Nasal polyps: Nasal cavity with bleeding necrotic nasal polyps, if the polyp breaks out of the infection and inflammation is likely to appear in the nose suddenly nosebleed phenomenon. In addition, high blood pressure, lack of vitamins, nasal malignant tumors and blood system diseases, can cause sudden nosebleed, the patient should go to the regular hospital in a timely manner to find out the cause of the disease, under the guidance of the doctor for targeted treatment.