Very effective.

Latex condoms have been tested and retested by manufacturers, researchers and the U.S. Food and Drug Administration to make sure you are getting great protection.

And you are! When you use a condom correctly each time you have sex, you are getting a lot of help from your little friend. Just check out these facts (and, for you skeptics, the research behind them):

Latex condoms are highly effective in preventing the sexual transmission of HIV during vaginal, oral, or anal intercourse.

You may be interested to know that in a two-year study of couples in which one person was already infected with HIV and the other person wasn't, not one uninfected partner contracted HIV when the couple used condoms correctly each time they had sex.

When used correctly, latex condoms are 98-percent effective at preventing pregnancy, and highly effective at preventing most sexually transmitted diseases (STDs), including chlamydia, gonorrhea, herpes and syphilis.

Have you ever heard that condoms are "porous"? It isn't true. Latex is resistant to the small viruses and bacteria that cause STDs. This means that even though viruses and bacteria are very small, they still cannot pass through latex condoms.

Using condoms lowers women's risk of human papillomavirus (HPV) infection and of developing cervical cancer, a disease associated with HPV. Consistent use of condoms can also help people clear HPV infection and/or reduce their risk of re-infection.

What you may not know about HPV is that many people's bodies naturally defeat this virus and "clear" it from their system. When a woman who has been exposed to HPV uses condoms with her partners, she reduces their exposure to HPV, which allows her body to more successfully fight off and clear HPV.

Why are condoms so great at preventing most STDs?

Because they prevent partners from sharing fluids, such as semen and vaginal fluids, and they prevent skin-to-skin contact between partners in the places they are most likely to have STDs, such as on the shaft of the penis or a woman's labia.

Condoms lower your chances of getting or giving a skin-to-skin STD, such as herpes or HPV, but they can't completely eliminate the risk. Condoms can't prevent infections from spreading if a person has an infection on the skin not covered by the condom. For example, if a person has a herpes sore on their upper thigh, then his or her partner could rub against it and also become infected with herpes.

But if you're going to have sex, using a condom is definitely better than nothing. For condoms to be most effective, they must be used correctly and consistently everytime you have oral, anal or vaginal sex. Correct use means following these steps every time.

1. Check the expiration date. This should be clearly printed on the box and on the condom wrapper.

2. Before you are ready to use the condom, keep it in a cool, dry place, so as not to damage it. In practical terms, this means that you shouldn't keep condoms in your pocket or wallet for a long time. Backpacks and purses are better places.

3. When you are ready to have sex, open the package carefully (watch your fingernails!), and remove the condom.

4. You will find that it is rolled up, and at this point you need to differentiate the inside from the outside. How to tell? You can make the condom look like a sombrero--with the thick, rolled-up part on the outside--so that you can roll it easily over the erect penis.

5. After you know which side of the condom is the inside, you need to make sure there is space at the top, and if there is a nipple at the top, that it isn't full of air. This will allow semen to collect in the reservoir at the top, and will prevent the condom from breaking.

6. Pinch the tip of the condom to squeeze the air out of the condom. This is important, because if the air is not squeezed out, the condom could break.

7. Place the condom on the tip of the erect penis and roll it all the way down to the base of the penis.

8. You need to use a condom for all three types of sex: vaginal, oral, and anal.

9. After ejaculation, hold the condom at the base of the penis and withdraw the penis. Carefully remove the condom from the penis, making sure that none of the semen seeps out.

10. Wrap the condom in a tissue and throw it away; do not flush it down the toilet.

11. Never reuse a condom!

12. And one final thing: When using latex condoms, always use only water-based lubricants, such as K-Y Jelly, Astroglide, or Slippery Stuff. Using an oil-based lubricant, like lotion or massage oil, weakens the latex and causes condoms to break.

Consider practicing this on yourself (if you're a guy) or on an object (if you're a girl), so that you'll know exactly what you're doing. When used correctly and consistently, condoms are 98 percent effective at preventing STDs and pregnancy!

Do you know how to use a condom correctly?  Real Teens, Real Life has two great animations all about how to use condoms correctly: Marvin the Condom and Condom Use Game. Test your skills!

Got a question about STDs? Call the CDC's national hotline at 1-800-227-8922, open 24/7.