The testicles (testes) are factories for making sperm, and the scrotum is like an air-cooled radiator that keeps the testicles at the best temperature for making sperm. About 2–3°C lower than normal body temperature seems optimum, which is why the scrotum hangs outside the body.
What makes testicles move upwards?
The testicles are connected to the inside of the groin by a muscle called the cremaster muscle. (The name cremaster is Greek for ‘suspender’.) The cremaster muscle can pull the testes upwards towards the groin. 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.
Protecting the testicles. Although the testicles 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 testicles out of harm’s way. When experiencing sudden danger, or even hearing about gory accidents, men often experience a contraction in the scrotum, a feeling that the testicles are being pulled upwards.
The cremaster reflex can also protect the testicles from over-cooling, by drawing them upwards into the cosy groin if the environment becomes too cold. Doctors reported a case of a 25-year-old-man who repaired commercial fridges. He had pain in his testicles whenever he worked inside a fridge.
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.
What is normal?
A testicle temporarily pulled up by the cremaster muscle (normal) should not be confused with an undescended testicle (abnormal). The main point is whether each testicle is in the scrotum except when temporarily pulled up. If your testicle is not in the scrotum normally, or you are not sure, you should see your doctor. For more information, look at our section on undescended testicles.
Written by: Dr Margaret Stearn
Edited by: Dr Margaret Stearn
Last updated: Tuesday, January 3rd 2017
For more information, Dr Phil Hammond discusses 'plums', 'peas' and varicocele in his Expert guide to scrotal lumps video below.
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