The most common source of vicarious menstruation is:

Vicarious menstruation is a rare condition in which extragenital bleeding occurs at regular intervals corresponding to menstrual period. The commonest form of vicarious bleeding is epistaxis and this is a feature in 30% cases. Other sites affected are alimentary tract, lungs, breast, gums, lips, kidney, rectum, retina and conjunctiva. It occurs most often at the extremes of menstrual life and in individuals with nervous and vascular instability. It ceases with menopause. The epithelium over the inferior turbinate bones is already influenced by estrogen and so epistaxis is most common form of vicarious menstruation.'