Bleeding may occur spontaneously but more often it results from forceful nose blowing and sneezing that increases venous pressure in the more vascularized nasal septum. Viral respiratory infections, such as measles, infectious mononucleosis, and influenza, may also predispose children to nosebleeds. Nosebleeds in children with these infections are more common in areas of low humidity. Allergic rhinitis with inflammation and subsequent drying may also lead to nosebleeds. Foreign bodies may cause direct trauma or pressure necrosis to the vessels of the nasal mucosa.
External trauma can cause either tears to the nasal mucosa or nasal fractures.
If bleeding from mucosal vessels occurs but the mucosa remains intact, a septal hematoma may develop. Abscess formation or septal perforation may occur if the septal hematoma is not drained. Although nosebleeds are usually benign conditions, they may be the first sign of serious illness. Persistent or recurrent nosebleeds with no obvious cause should raise the suspicion of bleeding disorders. Thrombocytopenia is the most common coagulation defect causing nosebleeds.