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They Can Take the Heat

Study: Researchers looking for male birth-control methods add fuel to the boxers-versus-briefs debate by finding that even polyester-lined underwear doesn't raise temperatures enough to inhibit sperm production.


Fertility doctors often advise men who are having trouble helping their partners to conceive to switch from briefs to boxer shorts to increase sperm production.

Fertility doctors, it turns out, may be wrong.

A new study by researchers at Harbor-UCLA Medical Center shows that wearing athletic supporters lined with polyester or even polyester impregnated with aluminum does not raise testicular temperature enough to inhibit sperm production significantly.

The results give the lie to the old wives' tale about briefs. Unfortunately, they also suggest that raising testicular temperatures as a means of birth control may not be a practical approach to the problem.

Sperm production is unusually sensitive to temperature--so much so that the testicles are stored in their own container outside the body. Their location in the scrotum allows their average temperature to be maintained at about 94 degrees, compared to the average body temperature of 98.6 degrees.

Dr. Christina Wang and her colleagues at Harbor-UCLA are looking for new forms of male birth control. The only currently used techniques both have significant problems. Condom use is associated with 10 to 15 pregnancies per 100 women in the first year of use, while vasectomy has a permanence that is not attractive to most men.

Raising testicular temperature by a simple physical technique "would be an attractive contraceptive approach because it would be inexpensive, would require minimal provider supervision, and would not involve administration of medicinal agents," Wang and her colleagues wrote in a recent issue of the journal Fertility and Sterility.

Other researchers have demonstrated that manually forcing the testes back into the body cavity and holding them in place with an elastic band can reduce sperm production to near zero. Sperm production was fully restored within four to eight months after cessation of the treatment. This technique could be used by only some men, however.

Athletic supporters lined with insulating oilcloth also significantly reduced sperm production, but were not comfortable. Immersion of the scrotum in hot water several times a day also reduced sperm production, but is not particularly practical.

Wang and her colleagues hoped to demonstrate that a less drastic form of warming might also provide effective male birth control. They recruited 21 healthy men between 23 and 44 who were divided into three groups.

The three groups were studied for six weeks to establish baseline scrotal temperatures and sperm counts. The first group was then asked to wear a cotton athletic supporter lined with polyester, which retains heat better than cotton. The second group wore athletic supporters lined with two layers of polyester, while the third wore supporters lined with one layer of polyester and one layer of aluminum-impregnated polyester.

To their disappointment, the researchers found that the average scrotal temperatures rose by only 1.5 to 1.8 degrees. Even at that increased temperature, semen volume, sperm concentration and sperm viability were all unaffected.

And if polyester-lined athletic supporters do not raise scrotal temperatures enough to impede sperm production, it is a sure bet that simple cotton briefs will not do so.

The team is now searching for other lining materials that would raise scrotal temperature more and still remain comfortable.

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