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The Straight Dope



Get a load of this clip from the Washington Times. It says the latex used in condoms contains pores through which HIV, the AIDS virus, can readily pass--suggesting that "safe sex" using a condom may not be very safe. What gives? Answer quickly. Lives are in the balance! --M.L., Chicago

I'll say. Your clip is a 1992 letter to the editor from Mike Roland, editor of Rubber Chemistry and Technology, a publication of the American Chemical Society. Roland argued that "the rubber comprising latex condoms has intrinsic voids [pores] about 5 microns (0.00002 inches) in size. Since this is roughly 10 times smaller than sperm, the latter are effectively blocked. . . . Contrarily, the AIDS virus is only 0.1 micron (4 millionths of an inch) in size. Since this is a factor of 50 smaller than the voids inherent in rubber, the virus can readily pass through."

This sounds scary, but there are a couple problems with it. First, Roland bases his statement about a 5-micron latex pore size on a study of rubber gloves, not condoms. The U.S. Public Health Service says that condoms are manufactured to higher standards than gloves. Condoms are dipped in the latex twice, gloves only once. If just 4 out of 1,000 condoms fail a leak test, the whole batch is rejected; the standard for gloves is 40 out of 1,000. A study of latex condoms by the National Institutes of Health using an electron microscope found no holes at a magnification of 2000.

The second problem with Roland's letter is that it suggests, at least to the casual reader, that condoms offer no protection at all against HIV. That's not so. Roland himself estimates that condoms reduce HIV transmission risk by a factor of three. He cites a 1993 analysis by S.C. Weller suggesting that condoms are 69 percent effective in preventing HIV transmission.

The government's counterargument to this is that Weller didn't distinguish between consistent and inconsistent users of condoms. Government spokesmen cite two European studies of "serodiscordant" heterosexual couples--that is, one partner had HIV, the other didn't. One study found that among couples using condoms consistently there were zero cases of HIV transmission between the partners. Inconsistent users had a 10 percent infection rate. The other study found an infection rate of 1.1 percent between consistent users, 5.7 percent between nonusers. In other words, consistent use of condoms reduced HIV transmission risk by a factor of five, conservatively speaking.

We could argue about these numbers, but let's put this in perspective. Roland thinks condoms reduce AIDS risk by a factor of 3. A study cited by the government says they reduce it by a factor of 5. It's believed avoiding high-risk sex partners reduces it by a factor of 5,000.

In short, regardless of who's right about latex, you'd be foolish to make condoms your only defense against infection. Abstinence--or, more realistically, avoidance of high-risk sex partners--is a far more effective strategy. (If you're a gay male and thus in a high-risk group to start with, at least stay away from IV drug users.) On the other hand, condoms do offer substantial protection, and if you insist on having sex with a high-risk partner, they're a lot better than no protection at all.

Does the rain in Spain in fact fall predominantly on the plain? --David English, West Somerville, Massachusetts

Mainly. But what I want to find out is whether the snow at Saint Lo improves the Bordeaux, the hail at Yale's on the Richter scale, and the sleet in Crete completely eats. You find out, you let me know.

Art accompanying story in printed newspaper (not available in this archive): illustration/Slug Signorino.

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