What cause a nose bleed ?

Many things: Nose bleeds can be spontaneous if the nasal passages are too dry. Nose bleeds can occur from nose picking, trauma from probing into the nose and direct trauma. Less common causes are in relationship to the menstrual cycle, and sometimes due to uncommon nasal tumors such as polyps. If you have these recurrently, then you should see an ENT doctor for a better diagnosis and treatment.