How effective are condoms? – includes information on how to use condoms and tips for condom care – Condoms – Now More Than Ever
Laurie Liskin
Condoms can prevent both pregnancy and sexually transmitted diseases (STDs). Laboratory studies show that sperm and disease-causing organisms cannot pass through an intact latex condom. Epidemiologic studies of condom users confirm that condoms can be very effective. Most studies, however, find that couples relying on condoms are, on average, not as successful at preventing unwanted pregnancy as users of most other family planning methods. Similarly, a substantial number of people relying on condoms to avoid STDs contract them nonetheless.
Laboratory Studies
Laboratory studies prove that sperm and disease-causing organisms cannot pass through intact latex condoms. Most condoms are only about 0.3 to 0.8 mm thick. Yet they normally contain no holes, even of microscopic size. A sperm has a diameter of 3 microns (.003 mm). STD-causing organisms are much smaller–from 1/4 to 1/70 the size of sperm. Still, laboratory tests show that none can penetrate an intact latex condom. This includes HIV, which causes AIDS (67, 68, 185, 314, 354). In contrast, disease-causing organisms sometimes can pass through condoms made from lamb’s intestine, often called natural skin condoms (237), but relatively few of these condoms are made.
Effectiveness Against Pregnancy
Best observed effectiveness. Conventionally, studies of contraceptives have looked at two different measures of effectiveness–method-effectiveness and use-effectiveness. Method, or theoretical, effectiveness is the effectiveness of the contraceptive method when it is used correctly and with perfect consistency. In other words, method-effectiveness takes account only of technical failures of the contraceptive method–for example, sperm leaking through a hole in a defective condom. Method-effectiveness can be difficult to gauge. Therefore the best rates observed in actual use are often used instead (149). These rates are important to prospective condom users: they indicate the level of protection that condoms will provide if used correctly with every act of sexual intercourse.
Condoms can be nearly as effective as other methods. Small studies from Great Britain in the 1960s and 1970s reported very low failure rates–from 0.4 to 1.4 pregnancies per 100 woman-years of use (217, 269, 270). (“Woman-years” is the sum of the time that each woman participated in the study.) The lowest rate reported in a large study is 4.2 pregnancies per 100 women in the first year of use, seen in a prospective study of married British clients of family planning clinics (125). By comparison, voluntary sterilization, Norplant, injectables, and, when used correctly, oral contraceptives have best observed failure rates of about one pregnancy or less per 100 woman-years (379). Using a spermicide along with condoms for extra protection could be, in theory, about as effective as any of these methods (190).
Typical effectiveness. Use-effectiveness is the effectiveness of the method in actual use, taking into account both technical failures of the method and users’ failures to use the method consistently and correctly. Use-effectiveness rates reflect the typical, or average effectiveness of a method when used by large groups of people. These rates are important to public health practitioners: they suggest the impact that condoms will have on the fertility of condom users as a group. Use-effectiveness rates are important to prospective condom users, too: they suggest the chances of pregnancy if the user is no more conscientious–or no less fertile–than average.
Typical pregnancy rates among condom users are 10 to 15 pregnancies per 100 women in the first year of use (129, 379). These failure rates are higher than for other methods in most studies. For example, an analysis of major developed-country studies estimated that the first-year pregnancy rate among condom users was 12 per 100 women compared with 3 for oral contraceptives, 6 for IUDs, and less than one for voluntary sterilization, but 21 for spermicides (379).
Worldwide, condom effectiveness rates vary greatly in various studies and among groups within studies, as Table 3 shows. In general, older, married couples who have used the method for some time and are strongly motivated to avoid pregnancy are the most effective users. This is true for nearly all contraceptive methods. Older couples generally are less fertile and have intercourse less often than young couples. At the same time, they may be comfortable with each other as sexual partners and have made using condoms a regular part of lovemaking.
Married, older, long-term users are not the only ones who can use condoms effectively, however. People who have sex infrequently or unexpectedly often use condoms. In this role condoms can be very effective, partly because coital frequency is low in these circumstances. For example, in an Israeli study of two groups of adolescent women relying on condoms, pregnancy rates were 2.1 and 4.8 per 100 women in the firts 12 months (127).
[TABLE DATA OMITTED]Protection Against Disease
Just as condoms can be very effective in preventing pregnancy, they also can protect against a wide range of STDs. Studies in the 1970s and early 1980s demonstrated that condoms help to protect against gonorrhea, syphilis, and mycoplasmas (23, 47, 162, 229, 271, 348). More recent studies have confirmed some of these findings and added to the list chlamydial infection, trichomoniasis, herpes simplex, and, most important, the AIDS-causing HIV (19, 79, 101, 102, 183, 254, 258, 323, 327, 340, 388).
Just how effective is condom use against STDs? Measuring this is harder than gauging its effectiveness against pregnancy. First, infectiousness varies among the different STD organisms. Second, few large studies have been conducted. Third, many STD-prevention studies involve people treated at STD clinics or clients of prostitutes–people clearly at high risk of infection. An overall estimate, however, can be drawn from a recent analysis for the World Health Organization (WHO), combining data from nine published studies. This analysis found that condom users faced a risk about two-thirds that of nonusers of developing gonorrhea, trichomoniasis, or chlamydial infection (322). Condoms offer less protection against STDs, such as herpes simplex, that can cause lesions in places not covered by condoms.
Protection against AIDS. Combining data from 10 studies of HIV transmission, the same analysis found a relative risk of about 0.4 for condom users (322)–less than half as great a risk as for nonusers. Just as in family planning studies, many of the participants in these studies did not use the condom consistently or, in some case, correctly.
In the long-term, condoms help prevent AIDS not only by blocking HIV but also by protecting against other STDs. People with STDs, particularly those that cause genital ulcers–chancroid, genital warts, herpes simplex, and syphilis–are two to seven times more likely to become infected with HIV than people who have not had STDs (40, 140, 203, 280, 349, 350).
Protection for women. Because condoms help to prevent STDs, they also help prevent two potentially life-threatening conditions in women that result from STD infection–pelvic inflammatory disease, which in turn can lead to infertility, and ectopic pregnancy (pregnancy outside the womb). In a 1982 study women relying on condoms faced a risk of pelvic inflammatory disease that was 40% of the risk faced by other women (187). Similarly, a recent study found that, when women’s sexual partners had used condoms for at least one year, their risk of having an ectopic pregnancy was 75% of the risk faced by women using other or no contraceptive method (211).
Condom use also helps to protect women against cervical cancer, which is thought to be caused by a sexually transmitted virus. In a recent study at least one year of condom use cut the risk of cervical cancer in half (351).
Why Failures?
If condoms can be so effective in preventing pregnancy, why are the average observed rates both for pregnancy and STD
[TABLE DATA OMITTED]infection so much worse? Limited evidence suggests that the individual, not the condom, is usually responsible for infections and unwanted pregnancies.
Inconsistent use. After all, condom use places a considerable burden on the user. It requires not just the man’s consent but usually also his initiative. Not facing unwanted pregnancy himself, he may not be motivated to put on a condom, which he must do in the midst of sexual arousal. And, for protection against disease at least, he must use a condom at each and every act of intercourse.
As a result, most couples apparently do not use condoms every time they have intercourse. Data are few, however. In Bangladesh only about 60% of men who said that they were using condoms for contraception used them at every act of intercourse (7). In Barbados even fewer men–only 30%–used condoms every time (329). Inconsistent use accounts for a large proportion of unwanted pregnancies among condom users (360).
Incorrect use. Incorrect use may explain some pregnancies and infections among condom users. Some mistakes may cause tears or lead to breaks: unrolling the condom before putting it on, trying to put on the condom with the rolled rim held toward the body rather than away from it, snagging the condom with fingernails or rings, and reusing condoms. Other mistakes allow unprotected contact: starting intercourse and then withdrawing to put on the condom, and not holding the condom rim while withdrawing after ejaculation, allowing the condom to slip off and spill semen. Little is known about how often these mistakes occur.
Breaks. Still, condoms sometimes do break. With AIDS drawing new attention to the condom, studies of condom breakage have been undertaken recently.
Prospective studies have reported breakage rates ranging from less than 1 to 12 per 100 during vaginal intercourse (see Table 4). Retrospective studies, although less reliable because they depend on users’ recall, report results in the same range (7, 10, 69, 131, 151, 374, 393). Rates for anal intercourse are also in this range (69, 131, 313, 374, 393). Nearly all of these studies are small, and the participants are self-selected.
Also, it is important to remember that a broken condom does not always lead to pregnancy or infection. A woman is fertile only a few days in each menstrual cycle. Her chances of pregnancy from any one act of sexual intercourse have been estimated to average 2 to 4% (373). In one US survey women reported 430 condom breaks, resulting in 19 pregnancies, or one pregnancy for every 23 breaks (151).
Although infection with an STD can occur at any time, most exposures in fact do not lead to infection. The chances of infection with HIV after a single sexual exposure have been variously estimated at less than one in 1,000 to one in 10, depending on whether the transmission is male to female, female to male, or male to male and whether the exposed person has genital ulcers (15, 41, 262).
In addition, not all condom breaks are equally risky. Some studies count breaks that occurred while the condom was being put on or taken off–clearly less risky than breaks during intercourse itself. In a North Carolina study more than half of the 7% breakage rate occurred before or after sex (276). Also, breaks or tears that occur along the sides or at the base of the condom may not release much semen. In the North Carolina study only one-third of the breaks occurred at the tip of the condom.
Breakage rates differ substantially among areas. For example, in clinical trials of newly made condoms, 2.5% of those used in Mali broke compared with 10.5% in Ghana (177). Indeed, condoms from the same production lot broke more often in Barbados and St. Lucia–13% and 10%–than in the US two years later–7% (276, 329).
Breakage rates also differ markedly among couples (7, 109, 136, 276, 408). For example, among six volunteers testing new and aged condoms, one volunteer accounted for almost half of all condom breaks (117).
A mix of reasons may explain the variation:
* Differing sexual behavior and sexual practices,
* Differing experience with using condoms,
* Whether users apply a lubricant that damages, the condom,
* Whether condoms were weakened by poor conditions in storage or shipment, and
* Whether the condom was made with a weak spot, hole, or other defect.
Sexual practices such as the length and vigor of intercourse may make a difference. In one study men broke condoms more often with their girlfriends than their wives (177).
Experience with condoms also could be important. One study has found that inexperienced users reported more broken condoms (151), although several others have found no difference (177, 276). In several Carribean countries men who could correctly put a condom on a penis-shaped model reported having fewer broken condoms in the past than men who had less skill putting the condom on the model (236). Insufficient vaginal lubrication may contribute to condoms breaking–a problem that could often be remedied by longer sexual foreplay (432). A preference for “dry sex,” reported in many areas, may contribute to breakage. At this point, however, little is known about how sexual behavior and skill with condoms affect breakage, and more research is crucial.
Mineral and vegetable oils substantially weaken latex in five minutes or less (402). These oils are found in common products such as petroleum jelly, skin lotion, and cooking oil. Unfortunately, many people unknowingly use these products to lubricate condoms (276). Products that contain water instead of oil–for example, glycerin, egg white, and K-Y Jelly–do not damage latex. Neither does spermicidal jelly or foam, which doubles as a lubricant and a source of extra protection but may cause irritation if used very often. (It is not clear whether some solid spermicidal inserts, tablets, or suppositories damage latex; more research is needed.) Some of the safe lubricants are hard to find or expensive in some places, however. Condom programs need to identify inexpensive, easily obtained materials that people would like to use as lubricants and that do not damage latex. Providers can test potential lubricants by rubbing them on a condom and checking an hour later for damage (71).
Exposure to ultraviolet light, heat, humidity, and ozone makes latex deteriorate and weakens condoms (21, 115, 117, 118, 402). The longer condoms are exposed to these conditions, the more easily they break, and once a package is cracked or torn deterioration is rapid. A 1986 study of Indonesian volunteers found that 7% of newly made condoms broke during intercourse compared with 20% of condoms that had been exposed to ultraviolet light for 10 hours and 49% of condoms that had been stored in a tropical climate for 42 months (115).
Occasionally, a condom breaks because of a manufacturing defect. Condoms are made according to national or international standards, and sample condoms are tested to assure high quality (see pp. 27-30). Only samples can be completely tested, however, because the tests for strength destroy the tested condoms. Sampling procedures limit the risk that a batch of condoms with more than a defined percentage of defects will reach users. But production cannot be perfectly uniform, and therefore the standards permit a small percentage of the sameple condoms to fail each test. Logically, then, manufacturer’s defects explain some breaks and leaks, but the number should be low.
A few studies have tried to sort out these various causes of breakage. A group of 34 male and female prostitutes in Australia reported only eight breaks in 1,269 acts of vaginal and anal sex–a rate of 0.6%. In seven of the eight breaks, the users accidentally tore the condom with fingernails or rings or else used an oil-based lubricant. Thus only one break could be attributed–by default–to a defective condom. This one represents less than one-tenth of 1% of all condoms used (313). In contrast, a British study reported that 5.3% of condoms broke during anal intercourse between homosexual men. More than two-thirds of the breaks occurred even when the users handled the condoms carefully and used only water-based lubricants (131).
Clearly, much more research is needed into condom effectiveness. Many questions need answers: What makes some people more effective condom users than others? How big a problem is sporadic use? How big a problem is incorrect use? Do some sexual practices risk breaking condoms? What are easy-to-find, safe lubricants? Are people getting deteriorated condoms that break? How often do new condoms break due to defects? Answers to all these questions will help programs design condom promotion, information, and counseling efforts.
COPYRIGHT 1990 Department of Health
COPYRIGHT 2004 Gale Group
