Dr Margaret answers emailers’ embarrassing problems
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Retractile testicles

Dear Dr Margaret
On occasions, my testicles are tending to climb up into my body after sex. Is there something wrong?

The testes (testicles) are connected to the inside of the groin by a muscle called the cremaster muscle. (The name cremaster is Greek for ‘suspender’.) This muscle is capable of pulling the testes upwards towards the groin, exactly as you have experienced. This is a reflex reaction, which means you can not control it consciously. In children, the reflex is very strong, but it lessens in the early teens.

Keeping cool
The testes are factories for making sperms, and the process seems to be very sensitive to temperature. A temperature about 2–3 oC lower than normal body temperature seems optimum, and this is approximately the normal temperature in the scrotum. In other words, the scrotum is like an air-cooled radiator that keeps the testes at the best temperature for making sperm. Truckers and other professional drivers sometimes have lower sperm counts than other men, probably because sitting in the driving seat for long periods keeps the testes too warm. We know this from some French research. The researchers attached skin temperature monitors to the scrotums of nine men, and found that after driving for 2 hours the scrotal temperature increased from 34 oC to over 36 oC.

Protecting the testes
Although the testes are happiest in the slightly cooler temperature in the scrotum, this is a vulnerable position. They are not very well protected here. So the cremaster reflex probably developed as a way of quickly pulling the testes out of harm’s way. Men often experience a contraction in the scrotum when experiencing sudden danger, or even hearing about gory accidents. There was some correspondence in the New Scientist magazine about this a few years ago. One man described contractions in the scrotum when driving at night in his low-slung sports care whenever a large rock loomed ahead. I have also read that Sumo wrestlers can train themselves to draw their testes up for protection during competition, but I do not know if this is true.

The cremaster reflex can also protect the testes from over-cooling, by drawing the testes upwards into the cosy groin if the environment becomes too cold. Doctors reported a case of a 25-year-old-man who repaired fridges. He had pain in his testes whenever he worked inside large ‘walk-in’ refrigerators. The doctors found he had an unusually powerful cremaster reflex.

Not a serious problem
Although children have a strong cremaster reflex, it tends to disappear or weaken by adulthood. In many men, the occasional contraction in the scrotum is just a ghost of the childhood reflex. Some men (like the fridge engineer) retain a strong reflex, and you may be in this category. One of the ways of triggering the reflex is touching the skin of the inner thigh, so it is not surprising that it could be related to sex.

A testis temporarily pulled up by the cremaster muscle (normal) should not be confused with an undescended testicle (abnormal). The main point is whether each testis is in the scrotum except when temporarily pulled up. Anyone whose testicle is not in the scrotum normally, or who is not sure, should see their doctor. You will find more information in the section on undescended testicle.

Sources of information
Bujan L, Daudin M, Charlet JP, Thonneau P, Mieusset R. Increase in scrotal temperature in car drivers. Human Reproduction 2000;15:1355–7.

New Scientist 1997;154(2078):97.

Scott BW, Gough MJ. Refrigeration engineer's testis. British Journal of Urology 1990;65:213.

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