Heat damage can affect sperm production or spermatogenesis within the testes. The testes hang outside the body and the reason for this is that sperm production is very sensitive to temperature changes. By hanging outside the body there is a cooling effect on the testicles, so they do not get damaged by heat. Another mechanism of cooling the testes down is by way of the pampiniform plexus of veins, which run from the testicle back to inside the body. These veins are able to divert the heat from the testicles so that the testes are not overheated. 


Sperm production


Normal sperm production takes about 72 days. There are however a number of other causes for fertility and it is interesting to note that over many years it is quite clear that the semen quality of men in general has declined but interestingly there has also been a causal relationship with an in the increase in the risks of testis cancer. It is therefore particularly important to examine and look for signs of testis cancer in men with fertility problems. In particular those men who have had a history of undescended testis should be evaluated and taught to regularly examine themselves. Men with infertility problems seem to have an increased risk of testis cancer in general.

Other causes of fertility problems include hormone problems, dietary problems, environmental toxins, trauma or surgery to the testis, which can result in men not being able to produce sperm at all in some cases.

There are a number of other causes of heat damage to the testes, one of which is called undescended testis as mentioned above. Men may be born with either one or both testicles not descended into the scrotum at birth. They are usually fixed into the scrotum at a younger age or even in some cases only found to be in the wrong place in adulthood. The longer the testicles are left undescended, the worse the effects on fertility. It is thought that the heat damage of the testicle being within the abdomen results in impaired sperm production. Certainly men with undescended testes can have fertility problems even if this is only on one side. 

There are other causes of heat damage to the testicles but what must be made clear, is that the evidence for some of these factors as causal agents is limited. This is because studies have either been done in animal experiments or the number of patients within the studies is small and so drawing conclusions can be difficult. Some of the other factors that may increase the temperature of the testes and have been associated in studies of causing fertility problems or changes in the sperm count, include hot saunas or hot baths, laptop usage, some occupations and cycling.

Exposure of the testis to heat e.g. saunas has been shown cause problems in sperm production but is reversible. Equally hot baths may also reduce fertility potential. 

In terms of laptop use, the theory is that the use of a laptop in close proximity to the genital area, for example in the seated position, may result in increased scrotal temperatures of up to 2.1ºC. However, it is unclear whether the laptop usage will affect sperm production. 

In theory, cycling has been argued to increase the temperature in the sitting position, but the evidence for cycling impairing sperm production is limited.

In Certain occupations e.g. welders or bakers who are exposed to increased heat stress, may also have fertility issues. 

Perhaps one of the most common causes of heat damage which has been associated with fertility problems and sperm production are varicoceles or varicose veins of the testicle. These are dilation of the pampiniform plexus of veins, that normally divert heat away from the testicles. It is unknown how the veins dilate but they can reach a considerable size, such that they can be seen when men are standing up. The situation is confusing as up to 15% of men who have normal semen analysis, will have varicose veins of the testicle or a varicocele. The figure however increases to about 40% in those men who have subfertility or fertility problems.




Varicoceles are thought to cause heat damage and release of toxins which may damage the sperm directly and also the DNA of the sperm which can result in problems with fertility. Evidence for fixing varicoceles is a controversial one and perhaps one of the biggest controversies in urology. However it is now becoming evident, in spite of previous evidence, that fixing varicoceles in certain patients may in fact improve not only the sperm quality and quantity but also reduce the damage to the sperm DNA. There is increasing evidence in fact that fixing varicoceles may in fact not only improve the outcomes from natural pregnancy but also the possibility of improving outcomes from assisted reproductive technology such as IVF/ICSI. 

It is very important to examine all men who have fertility issues or abnormal sperm tests so that these problems can be dealt with and excluded. 

What needs to be re-iterated however is more robust studies need to be performed to assess the role of heat damage to the testis, but there is enough evidence to suggest that excessive heat should be avoided to prevent damage to the testicles.