Barrier methods of birth control block sperm from entering the uterus. Using a spermicide with a barrier method gives you the best possible barrier method protection.

The spermicide kills most of the sperm that enter the vagina.
The barrier method then blocks any remaining sperm from passing through the cervix to fertilize an egg.
Barrier methods camera.gif include the diaphragm, cervical cap, male condom, and female condom and spermicidal foam, sponges, and film. Unlike other methods of birth control, barrier methods are used only when you have sexual intercourse. Be sure to read the instructions before using a barrier method. It is very important that you use a barrier method correctly every time you have sex.

Sexually transmitted infection protection

Male or female condoms are the only birth control methods that protect against sexually transmitted infections (STIs), including infection with the human immunodeficiency virus (HIV). To help protect yourself and your partner from STI infection, be sure to use a condom every time you have sex.

Risks
Condoms
A condom can tear when it is too tight or fall off when it is too loose. If this should happen while you are having intercourse, use emergency contraception. If you are worried about exposure to a sexually transmitted infection (STI), get tested.

Diaphragm or cervical cap
Using a diaphragm with spermicide may increase your risk of urinary tract infections.

Leaving a diaphragm or cervical cap in for longer than 24 hours increases your chances of getting toxic shock syndrome.

Spermicide
Some people are allergic to nonoxynol-9, which is the active ingredient in most spermicides. They can develop sores in the vagina or on the penis, which make it more likely that HIV can be transmitted from an infected partner during sex.

The U.S. Food and Drug Administration (FDA) warns that nonoxynol-9 in vaginal contraceptives and spermicides may irritate the lining of the vagina or rectum. This also increases the risk of getting HIV/AIDS from an infected partner.



References:
Barrier Methods of Birth Control