Studies have shown that latex condoms are highly effective in preventing HIV transmission when used consistently and correctly. These studies looked at uninfected people considered to be at very high risk of infection because they were involved in sexual relationships with HIV-infected people. The studies found that even with repeated sexual contact, 98-100 percent of those people who used latex condoms correctly and consistently did not become infected.

Although condoms have been in use since ancient times, Casanova was the first to popularize their use. They were at first made of linen or animal intestines, but at the advent of vulcanized rubber in the 1840's they took on the name "rubbers" and were mass-produced. There are many types of condoms available; most are made of latex rubber, but some are made from polyurethane or even animal tissue (e.g., "natural skin"). They may be lubricated, ribbed, or treated with spermicide, and may be purchased without a prescription. Condoms are convenient and easy to use. They can help both partners from giving each other sexually transmitted diseases (STDs).

The condom is a thin shield that is worn on the penis. It traps the semen expelled from the penis during intercourse, preventing sperm from entering the vagina. A man must put on a condom while he has an erection but before intercourse. Afterward, he should withdraw immediately to prevent leakage. Although condoms can be effective, they sometimes break during intercourse. For this reason it is suggested that they be stored in a cool, dry place; oil-based lubricants (such as Vaseline or baby oil) should not be used as they can weaken latex condoms. Even medication for female yeast infection can cause condom failure.

Condoms, especially the spermicidal variety, increase the risk of urinary tract infections in women. In fact spermicidal condoms have not been shown to be more effective than condoms without spermicide. Some men and women find the latex irritating due to allergy, and spermicidal condoms can worsen the allergenic properties of the latex. For sensitive individuals, non-spermicidal polyurethane or natural skin condoms may be more acceptable. Natural skin condoms, however, are expensive and do not protect against disease, and polyurethane condoms are more likely to break. Most men report reduced sensitivity during intercourse, some men find they cannot retain an erection when a condom is used, and condoms may affect the spontaneity of intercourse. When used consistently by married couples, condoms can be very effective, but failure rates are much higher for unmarried couples and teenagers.

If a condom is to be effective, the most important rule is to use it every single time. A new one must be worn if intercourse is repeated.