A small collar or ring of tissue located just inside the opening of the vagina where the vulva and vagina meet. The hymen is made from two different kinds of embryonic tissue, with one side being sensitive to testosterone and the other being sensitive to estrogen. As a girl approaches puberty and her body produces more estrogen, her hymen becomes more elastic. After puberty, the hymen often becomes more like an o-ring or a collar of tissue rather than a barrier. Researchers often have trouble distinguishing between the hymens of teenage girls who are sexually active and the hymens of teenage girls who are still virgins. The hymen can bleed during a first intercourse if it isn’t fully estrogenized (elastic enough) or if the lovemaking is clumsy. Hymens do not become worn down due to athletic activity. While the hymen may become less prominent with age, it never goes away.