The hymen is a tissue membrane located at the opening of the vagina. Hymens may differ in shape, but the most common hymen is shaped like a crescent moon, laying completely on its side. This shape allows for menstrual blood to flow out of the vagina and for a tampon to be inserted.
It is true that all girls are born with a hymen, but some are born with a hymenal abnormality. An abnormal hymen can block menstrual blood flow and cause pain or difficulty with tampon insertion/intercourse.
The most concerning hymenal abnormality is an imperforate hymen. This is when the hymenal membrane completely covers the opening of the vagina. Once a girl with an imperforate hymen starts bleeding and shedding her uterine lining, the blood remains trapped inside. It backs up into the vagina, and continues to distend the vagina with each subsequent cycle, until surgical intervention is done. This typically causes cyclic abdominal pain in pubertal girls around the age of 12 years and is diagnosed by ultrasound and genital exam.
Another type of hymenal abnormality is a microperforate hymen. This type of hymen is similar to an imperforate hymen, but has a small “micro” opening that allows menstrual blood to flow out. It typically does not allow for insertion of a tampon, but if a tampon can be inserted, it may not be able to be removed once it has expanded with blood.
The last type of hymen is a septate hymen. Its similar to a normal hymen, but has a band of tissue across the middle that separates the single vaginal opening into two. These patients often also have issues with tampon use, but are able to pass menstrual blood without issue.
All of these hymenal abnormalities are treated with surgery and the goal is simply to create a normal vaginal opening.
Finally, the hymen does not break at time of first intercourse or sexual debut. Sexual intercourse can cause the hymen to stretch or slightly tear (may have associated bleeding), but the idea that a membrane is broken at time of first intercourse is not true.
