The hymen (or maidenhead) is a ring of tissue around the vaginal opening. The term comes from a Greek word meaning "membrane", and is also the name of the classical Greek god of marriage. Although many people believe that the hymen completely occludes the vaginal opening in human females, this is not normally the case.

Historical significance
Because of the belief that sexual activity would usually tear this membrane, its existence has been considered a guarantor of virginity in societies that place a high value on female chastity before marriage. However, the hymen is a poor indicator of whether a woman has actually engaged in coitus because a normal hymen does not completely block the vaginal opening. The blood that is sometimes, but not always observed after first penetration can be due to tearing of the hymen or nearby tissues. These tears often quickly heal, and combined with the fact that the hymen is often broken through non-sexual activities or not present in some women at all [1], it should never be thought of as a sign of virginity or chastity.

Types
The size and shape of this opening (or openings) vary greatly from person to person. Some women are born with no hymen at all, while others have a closed or imperforate hymen. These women may require a gynecologist to perform a medical procedure called a hymenotomy to allow menstrual products to escape. Still other women have unusually thick hymens that may require a hymenotomy to prevent pain for the woman during sex. In a woman or girl past puberty, the general structure of the hymen can be compared to a scrunchie in that it is elastic and stretches open easily. Some other common forms of hymen are:

Annular – in which the hymen forms a ring around the vaginal opening.
Septate – in which the hymen has one or more bands extending across the opening.
Cribriform – in which the hymen stretches completely across the vaginal opening, but is perforated with several holes.
Parous Introitus – which refers to the vaginal opening which has had a baby pass through it and consequently has nothing left of its hymen but a fleshy irregular outline decorating its perimeter.

Development
During the early stages of fetal development there is no opening into the vagina at all. The thin layer of tissue that covers the vagina at this time usually divides to a certain extent prior to birth, forming the hymen. In a very small percentage of female births, this tissue has divided completely, and the baby is born without a hymen. Also, a woman can have the hymen surgically restored in order to feign not having engaged in intercourse. For these reasons, as well as the reasons detailed above, the presence or absence of a hymen cannot be taken as a reliable indicator of whether a woman has engaged in intercourse.

Cultural construction
In late 2005 Monica Christiansson, former maternity ward nurse and Carola Eriksson, a PhD student at Umea Unviersity announced that according to studies of medical literature and practical experience, the hymen should be considered a social and cultural myth, based on deeply rooted stereotypes of womens' roles in sexual relations with men. Christiansson and Eriksson support their claims by pointing out that there are no accurate medical descriptions of what a hymen actually consists of. Statistics presented by the two show that fewer than 30% of all women who have gone through puberty and have consensual intercourse bleed the first time. Christiansson has expressed an opinion that the use of the term "hymen" should be discontinued and that it should be considered an integral part of the vaginal opening.