A cervical cap is a small cup made of soft silicone or rubber that fits over the cervix, which is the part of the uterus that opens into the vagina. It is a form of barrier method birth control that blocks the sperm from entering the uterus and fertilizing an egg. The cervical cap covers the cervix, stopping sperm from joining an egg. It must be inserted deep inside the vagina before sexual intercourse to help prevent pregnancy. Suction helps it stay in place. The cervical cap is most effective when used with spermicide, which is a cream or gel that kills sperm. Adding spermicide to the cervical cap before inserting it into the vagina makes it much more effective. The cervical cap can be left in longer than a diaphragm, up to 2 days. However, it does not protect against sexually transmitted infections (STIs), so couples having sex must always use condoms along with the cervical cap to protect against these infections. The cervical cap is not usually recommended for most young women and teens because it can be very hard to insert correctly. Inserting and removing a cervical cap requires a girl to reach into her vagina to the cervix with her fingers.