Two French doctors recommend the ideal male contraceptive: underwear that holds a man’s testicles tightly against his body (1).

Do you know why a man’s testicles are located outside his body and a woman’s ovaries are inside her’s? Because the scrotum’s temperature is at least one degree cooler than body temperature. A normal body temperature of 98.6 degrees lowers sperm counts and prevents sperm from maturing normally (2). Some men have testicles that remain inside of their bodies, where the extra heat prevents them from fathering children. Some men have varicocele, large veins that surround their testicles to bring hot blood from the body and raises testicular temperature to makes them infertile (3). Sexual stimulation and desire does not raise sperm counts or motility of normal men or those with elevated scrotal temperature (4). The French doctors used special underpants that raised the temperature of the testicles by holding them tightly against the body and prevented the men from impregnating their wives. However, athletic supporters do not reduce fertility presumably because they are not worn continuously enough to keep scrotal temperature elevated all the time (5).

Twenty-five to 55 days after a man develops a fever, his sperm counts are reduced and do not return to normal for around 50 days. (6) Sitting in a sauna set at 180 degrees Fahrenheit for more than 30 minutes reduces sperm counts to cause temporary sterility. Exercise raises body temperature, but does not cause infertility. Doctors at Kent State University showed that people who exercise hard enough to raise their temperatures as high as 104 degrees for forty-five minutes a day for five straight days do not have reduced sperm counts, presumably because the temperature returned to normal as soon as the person stopped exercising (7). Infertility in Scotland will be rare as long as the men don’t wear anything else under their kilts.

By Gabe Mirkin, M.D., for CBS Radio News

1) L Bujan, R Mieusset. Male contraception by testicular heating. Contraception Fertilite Sexualite 1995(Oct);23(10):611-614.

2) Fertility and Sterility 1990 (October);54:694.

3) FR Parikh, SA Kamat, GG Kodwaney, D Balaiah. Computer-assisted semen analysis parameters in men with varicocele: Is surgery helpful? (yes) Fertility and Sterility 66: 3 (SEP 1996):440-445.

4) JH Vanroijen, AK Slob, WL Gianotten, GR Dohle, ATM Vanderzon, JTM Vreeburg, RFA Weber. Sexual arousal and the quality of semen produced by masturbation. Human Reproduction 11: 1 (JAN 1996):147-151.

5) C Wang, V Mcdonald, A Leung, L Superlano, N Berman, L Hull, RS Swerdloff. Effect of increased scrotal temperature on sperm production in normal men. Fertility and Sterility 68: 2 (AUG 1997):334-339.

6) Med Aspects of Human Sexuality 1980;14(9):121.

7) McConnell, T.R. and Sinning, W.E. Med Sci in Sports and Exercise 1984;16(1):51-55.