Heat and Sperm Quality

The Relationship Between Scrotal Temperature and Semen Parameters

The testicles are located in an exposed and vulnerable location outside of the body for a reason. This is because for optimal sperm production to take place, the testicles need to be 3.5 to 7 degrees F  (1.9-3.9 degrees C) cooler than the body’s core temperature. [Mieusset R. FertSteril 1995] Elevated scrotal temperatures have been found to have a detrimental impact on sperm production through multiple mechanisms including apoptosis (programmed cell death) of spermatogenic cells, increased oxidative stress, and sperm DNA damage. [Durairajanayagam D. ReprodBiomedOnline 2015]. Decreased semen parameters have been found in animal studies with increased heat exposure [Perez-Crespo M. MolReprodDevelop 2008] and human studies as well. [Thonneau P. HumReprod 1998]. Further evidence of an impact of heat on sperm quality is the well-documented decreases in sperm density around the world during the Summer months. [Jorgensen N. HumReprod 2001]

The body has many effective mechanisms to keep scrotal temperature at ideal levels, and it can handle most weather and exercise-related heat changes. In general, for every one-degree increase in ambient temperature, the scrotal temperature increases by only about a tenth as much. Still, despite these effective mechanisms, the testicles can be exposed to amounts of heat that cause problems with fertility. This section will review some common heat-related risk factors for decreased sperm quality.

Hot tubs and Hot showers and sperm quality

Exposure to wet heat has been associated with decreased semen parameters in men. An example is a 2007 study in which men using hot tubs with a temperature above 98.4 degrees for 30 minutes per week for 3 months were found to have a 22% lower sperm motility. [Shefi S. IntBrazJUrol 2007].

A common question is whether there is a “safe” temperature for hot tub or hot shower use. This question has not been definitively answered. However, if the testicles like to be at minimum 3.5 degrees (1.9C] cooler than the normal body temperature of 98.6 degrees [37C], then a general goal to shoot for would be a temperature of less than 95 degrees [35C]. The average hot tub temperatures usually fall within the 97 to 104 degree range [36-40C]. In terms of hot showers, the discomfort threshold for hot water is about 106 degrees [41C] in most people. Therefore, very hot showers also have the potential to be damaging to sperm as well. In general, warm showers/baths are fine, but if a man is steaming up the bathroom with his shower or bath then he may want to turn down the temperature.

Saunas

As opposed to hot tubs, saunas usually get up to very high temperatures with an average of around 180-195 degrees [82-90.5C]. These high temperatures have been associated with disruption of spermatogenesis [Jockenhovel F FertSteril 1990] and decreases in semen parameters. [Garolla A HumReprod 2013][Saikhun J. JAndrol 1998]. The bottom line is that saunas should be avoided in men who are having difficulties conceiving.

Laptop computer use and sperm quality

Other potentially problematic causes of heat exposure include laptop computers when used directly on the lap. Studies have confirmed decreases in semen analysis parameters when men use their computers directly on their lap. [Sheynkin Y HumReprod 2005]. Recommendations to mitigate the impact of lap top computers is to place the computer on a desk or put a thick barrier (such as a pillow) between the laptop and your lap so that you don’t feel any excess heat.

Car seat warmers and fertility potential

Heated seats directly increase scrotal temperatures and should be avoided in men with fertility issues. [Jung A. FertSteril 2008]

Boxers vs Briefs- do they really impact sperm quality?

When the testicles get warm, the response of the body is for the scrotum to stretch out. This helps to get the testicles further from the body’s elevated core temperature as well as provide an increased surface area for cooling. Multiple studies have documented potential improvements in semen parameters with the use of loose underpants. [Lynch R. FertSteril 1986][Tiemessen CH. Lancet 1996]. A 2018 study looking at 656 men found that those who wore primarily boxers had sperm counts which were 25% higher than those wearing tighter underpants. [Minguez-Alarcon L. HumReprod 2018]

The impact on male infertility by Sitting for Prolonged Periods of Time

Many jobs in today’s modern economy involve sitting for long periods of time whether in front of a desk computer terminal or in the cab of a long-distance truck or car. Increased scrotal temperatures have been documented in the sitting position as opposed to standing and walking. [Durairajanayagam D. ReprodBiomedOnline 2015]. Occupational drivers have been documented to have increased scrotal temperatures [Bujan L. HumReprod 2000] as well as lower semen parameters. [Chia SE. AnnAcadMedSingap 1994][Figa-Talamanca I. AmJIndMed 1996]. Potential strategies for dealing with sitting-related heat are to try and sit on a non-cushioned seat (if possible) and with your legs somewhat apart which can help lower scrotal temperatures. [Koskel OR. Pathophys 2005]. Loose boxer-type underpants can potentially help mitigate the impact as well as getting up every few hours to help cool the scrotal area. Standing desks for people who work at a desk may also be beneficial for office-based workers.

Heat Exposure at Work and the potential impact on sperm quality

In addition to the heat-related problems that are described for men who sit for prolonged periods of time at work, men who work in certain professions have significant heat exposure as well. Decreased semen parameters have been documented in bakers as well as ceramic oven operators. [Thonneau P. Lancet 1996][Figa-Talamanca I. ReprodToxicol 1992]. Military sailors exposed to extreme heat in submarines have also been noted to have decreases in sperm quality as well. [Velez da la Calle JF. HumReprod 2001]. Likely the best strategy in these situations is to wear loose boxer-style underpants to allow the body to utilize its own built-in cooling mechanisms.

Scrotal Cooling

Cooling of the scrotum has been proposed as a mechanism to manage the elevated scrotal temperatures of men at increased risk with their profession. Although scrotal cooling has not been extensively tested, a few small studies have shown evidence of some potential improvement in sperm quality. [Mulcahy JJ. JUrol 1984][Jung A. Reprod 2001]. Commercially, several products are available, including Snowballs (men’s briefs with pouches for re-freezable ice packs) and Fertilmate cooling patches. The practical use of these products is somewhat in question as how often would these types of cooling products need to be changed in men who are at the highest risk (and therefore the highest scrotal temperatures) during a normal 8 hour workday? Another product is the uBreeze which is a fan-based scrotal cooling device that plugs into a USB port and therefore designed for computer workers. Currently, routine use of scrotal cooling devices is not recommended from most male fertility specialists based on a few small studies from almost 30 years ago. More studies are clearly needed to see if scrotal cooling can help improve semen parameters in men at increased risk due to their occupation.