Harvard Men's Health Watch

Medical memo: Hot seats, laptops, and sperm

Every man who has put on an athletic supporter must have wondered why his "family jewels" are suspended in such a vulnerable position. Why hasn't nature tucked the testicles into the protective confines of the pelvis like their female counterparts, the ovaries?

In fact, early in embryonic life, the testicles are positioned deep in the rear of the abdomen. But at about the 17th week of pregnancy, the testicles begin to gradually descend through the abdomen. They arrive at the groin 5 to 10 weeks later, then cross into the scrotum by the 30th week of pregnancy.

There is a simple reason for this: temperature. Whether a man is hot or cool, his scrotal temperature averages about 5? F less than his internal body temperature. This low temperature is essential for sperm production. When conditions are right, a young man's testicles can crank out up to 1,000 sperm a second. But at warmer scrotal temperatures, sperm production slows, sometimes impairing fertility.

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