The bursting of blood vessels of the nasal mucosa causes nosebleeds. Most often it affects the nasal septum, the most anterior part of the nasal septum. At this point, a dense network of vessels (Locus Kiesselbachi) is found under a sensitive mucous membrane. Frequent blowing or picking the nose is extremely stressful and injures both the mucosa and underlying vessels.
Normally, nosebleeds are harmless; almost every adult has been affected by them at some point in his or her life. However, medical treatment is rarely necessary, e.g. in case of severe blood loss due to a coagulation disorder.