Dry Air or Nasal Trauma: This is the most common cause of nosebleeds (epistaxis) in adolescents. Dry air can cause the nasal mucosa to become dry and cracked, leading to bleeding. Minor trauma, such as picking or blowing the nose, can also cause bleeding.

Allergies or Infections: Allergic rhinitis or upper respiratory infections can cause inflammation and irritation of the nasal mucosa, leading to bleeding.
Nasal Septum Deviation: A deviated nasal septum can cause turbulent airflow, leading to dryness and irritation of the nasal mucosa, which can cause bleeding.
Hormonal Changes: Hormonal fluctuations during puberty can cause changes in the nasal mucosa, leading to increased bleeding.

Hypertension: Uncontrolled high blood pressure can cause blood vessels in the nose to become fragile and prone to bleeding.
Bleeding Disorders: Conditions such as hemophilia, von Willebrand disease, or platelet function disorders can increase the risk of bleeding.
Tumors: Although rare, nasal tumors such as angiofibromas or other malignancies can cause bleeding.
Vascular Malformations: Conditions such as hereditary hemorrhagic telangiectasia (Osler-Weber-Rendu syndrome) can cause abnormal blood vessels in the nose, leading to bleeding.

Granulomatosis with Polyangiitis (Wegener's Granulomatosis): A rare autoimmune disorder that can cause inflammation and bleeding in the nasal mucosa.
Sarcoidosis: A rare condition that can cause granulomatous inflammation in the nasal mucosa, leading to bleeding.
Foreign Body: Although more common in younger children, a foreign body in the nose can cause bleeding in adolescents as well.