Nosebleeds in teenagers may be caused by trauma, nasal septum disease, tumor, rhinitis, systemic diseases and so on. 1. Trauma: Trauma, surgery, etc. may cause damage to the nasal septum, sinuses, as well as the anterior cranial fossa and middle cranial fossa, all of which can cause nosebleeds. If the posterior lateral nasal artery ruptures or the intracranial internal carotid artery aneurysm ruptures, it will lead to severe nosebleeds. Violent coughing, blowing the nose too heavily, digging the nose too deeply, and excessive negative pressure during sinus negative pressure replacement can also cause the nasal mucosal blood vessels to rupture and bleed. 2. Nasal septum disease: the mucous membrane near the bony ridge or talar eminence or the convex surface of the deviation is relatively thin, the tension is relatively large, often due to the dryness of the mucous membrane, resulting in rupture and bleeding. The mucous membrane around the perforation of nasal septum is dry and eroded, which is also prone to bleeding. 3. Nasal cavity, nasopharyngeal, sinus tumors: patients with fibrous hemangioma, papilloma, hemangioma, etc., will also have nosebleeds, and often there will be hemorrhage. 4. Allergic rhinitis: patients with allergic rhinitis may have repeated episodes of nosebleed due to the abnormal secretion function of nasal mucosa and dryness of nasal mucosa. 5. Systemic diseases: Nosebleed may also be the first symptom of some systemic diseases, such as leukemia and other blood diseases, bleeding is mostly bilateral. In life, we should pay attention to keep the nasal cavity moist and prevent the mucous membrane from being damaged. Once a nosebleed occurs, it is recommended to go to the regular hospital in time, under the diagnosis of the doctor, and actively cooperate with the treatment.