The vagina is a muscular, highly expandable, tubular cavity leading from the vestibule to the uterus. The vagina is the structure penetrated during vaginal intercourse, and it serves as an exit channel for menstrual flow. The anterior vaginal wall is more densely packed with nerves and more highly sensitive to stimulation than the posterior vaginal wall.

The healthy vagina maintains a balance of various organisms called Lactobacillus or acidophilus. Vaginal infections happen when other organisms grow and change the normal balance of organisms in the vagina. This is sometimes caused by stress or following a course of antibiotics (which in addition to killing the infecting bacteria for which the antibiotics were persribed, kill the organisms that maintain the balance in the vagina.