Because the testes are held by the scrotum outside the body, they are usually a degree or two cooler than inside your body. In fact, sperm production is dependent upon a temperature 2°C to 4°C below the core body temperature.
It is generally assumed that the lower temperature leads to reduced rates of oxidative DNA damage and hence to fewer mutations in resulting sperm. In other words, a warmer scrotum means its contents will have to work harder to produce healthy sperm for conception.
An external source of heat such as a laptop computer placed close to the scrotum can significantly increase scrotal temperature, and it may impact negatively on future fertility. This is of particular concern because laptop computers are widely used by young men of reproductive age.
A 2010 study published in the journal Fertility and Sterility measured the scrotal temperature of men balancing laptops on their knees. The results suggested that even with a lap pad under the computer, the men's scrotums heated quickly. After one hour sitting with the legs closed, the testicle temperature had risen by up to 2.5°C. Yet previous research has found that testicular or scrotal temperature elevation above just 1°C was associated with a considerable negative effect on sperm cell development (spermatogenesis) and fertility.
The research also suggested that it took longer for the testicles to become overheated when men sat with their legs spread wide. This research does not suggest that laptop use will make you infertile. However, frequent use might not allow enough time for cooling between heat exposures, and it may contribute to changes in male reproductive function.
There are some strategies you can adopt to help minimise the influence of laptop computers on your fertility, including the following:
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References available on request