Some girls bleed the first time they have sex, but not all girls do. The reason some girls bleed the first time they have sex is because their hymen stretches or tears. The hymen is a very thin piece of skin-like tissue that partly covers the opening of the vagina.Make your tax-deductible gift now.Any day now, the Supreme Court could rule to restrict access to abortion.Help Planned Parenthood stand up for patients and protect our rights. Rush your gift today.