The female condom is a polyurethane sheath worn inside the vagina to prevent pregnancy and sexually transmitted diseases (STDs). It has two rings, one on either end, connected by a condom-shaped tube. One ring is inserted into the vagina, against the cervix, located at the back of the vagina. The other ring hangs outside the vaginal opening. This is where a guy's penis is inserted during intercourse.

Just like male condoms, female condoms can only be used once. Never use a female and male condom together. They could rub together and tear, and you'll end up with no protection.

When used perfectly, the female condom prevents pregnancy about 95 percent of the time. The typical (real world) rate is a lot lower - 79 percent - because they tend to be difficult to use. But if you can insert and use the female condom correctly, they also offer some protection against STIs because they cover part of the labia.

Again, like male condoms, they only prevent the spread of diseases that are passed through body fluids - HIV, gonorrhea, chlamydia, and syphilis. Some STDs, like herpes and genital warts, are spread through skin-to-skin contact. A female condom may not cover areas of the skin that are infected, such as the scrotum, labia, or even the inside of the thigh. So condoms - both male and female - can't protect against these kinds of infections.

The good news is that there are little side effects from female condoms. Some say the female condom slips or is uncomfortable during sex, especially if the rings rub or pull against the penis or the vagina. Some women, though, say the female condom stimulates the clitoris, a sensitive spot that most women need to have touched or rubbed in order to have an orgasm. Not many people are allergic to polyurethane, but if you are, using a female condom could cause itching and irritation.

The female condom is sold in drug stores and supermarkets under the name Reality without a prescription. They cost about $3 each.

For more information, click "Female Condom," or you can call the Sex Information Line at 1-888-30-SX-ASK (307-9275), open Monday through Thursday, 2-8 p.m. Pacific Standard Time.