MODEL RELEASED. Nosebleed. A six year-old boy with a nosebleed, wiping it onto a tissue. A nosebleed is caused by a loss of blood from the mucous membrane that lines the inside of the nose. Nosebleeds are most frequent during childhood and in old age. The most common cause of a nosebleed is a blow to the nose. Rarely, they will be a sign of an underlying disorder such as high blood pressure or a bleeding disorder. Nosebleeds are stopped by simple first-aid measures.