The hymen is a membrane, or thin area of tissue, that covers part of the opening of the vagina. It usually has an opening that widens as a girl approaches puberty.[1] An imperforate hymen is when the hymen covers the entire opening of the vagina, sealing it shut.[2] About 1 out of 2,000 women are born with this condition, which isn't caused by anything specific but just happens.[3] Girls with an imperforate hymen have to get it fixed with an easy surgery, after which it's like a regular hymen and should cause no more problems.[4]