Male Fertility and Heat
The testicles are located outside of the body because they need to be two to three degrees cooler than the rest of the body for optimal sperm production. 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.
How hot is too hot? There is no set answer to this that applies to everybody. As with any other male-factor issue, it varies by individual. However, studies have shown that taking a fairly hot bath or shower—over 104°F—can cause a reduction in sperm count or sperm quality in some men. For comparison, 104°F is often pre-set as the water temperature for many hot tubs. Temperatures in saunas are often above 150°F.
I recommend that men trying to have children avoid hot tubs, saunas, and hot baths, and to take warm but not hot showers.
Other potentially problematic causes of heat exposure include laptop computers when used directly on the lap. Some studies have shown that in as little as 10 minutes this can create enough heat to decrease semen parameters in some men. If you use a laptop, put it 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 in are another potential source of heat exposure. Don’t use them if you’re trying to conceive. And remember that the life cycle of sperm is about ten weeks, so if you’ve been exposed to any of these sources of heat, sperm quality may be impacted for the next two and a half months.
Boxers or Briefs?
This topic can be controversial, with different research articles showing findings that support both sides of the argument. Wearing tight underpants does appear to inhibit one of the body’s most effective natural mechanisms for scrotal temperature control. Normally, when the scrotum gets hot it stretches out, which increases its surface area. This both decreases scrotal temperature directly and provides a greater surface area for sweat to evaporate from, which also has a cooling effect. Tight underpants keep the scrotum from effectively expanding, and also press it against the warm body and inner thighs.
Wearing tight underpants shouldn’t make much of a difference for men who live and work in cool, temperature-controlled environments and do not sit for prolonged periods of time (see below). However, for men who spend a fair amount of time in warmer temperatures, tighter underpants can pose a problem, and for them I suggest boxers. Also, boxers may be of benefit to men in jobs that have significant heat exposure.
What about boxer briefs, which are not necessarily tight but do provide some support in the scrotal area? It depends on how the boxer briefs fit that particular man and the fabric out of which they are made. If the boxer-briefs are fairly tight and do not allow the scrotum to descend much when exposed to heat, then switching to regular boxers may be a good idea if you have significant heat exposure during the day.
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 computer terminal at a desk or in the cab of a long-distance truck. Prolonged sitting can increase the scrotal temperature to the point where sperm quality can become compromised in some men. When you’re sitting, the legs generally aren’t free to spread much; this traps the scrotum between the thighs, which can increase the scrotal temperature significantly. The position of the scrotum between the thighs can also prevent the normal relaxation of the scrotal skin, which the body uses to regulate scrotal temperature.
Studies have shown that the scrotal temperature can increase as much as 3 to 4°F when men drive for more than two hours at a time. Higher levels of semen abnormalities have been found in men who drive for long periods, such as taxi drivers. Longer times to pregnancy have also been shown to be associated with driving more than three hours per day.
If you sit for long periods of time, whether at a desk or while driving, wear loose-fitting underpants (such as boxers) and try to sit with your legs apart to increase air flow to the scrotal area. It may also be beneficial to get up and walk around for a few minutes every hour and a half to two hours during the day. While some men attempt to decrease scrotal temperature further with ice packs in the scrotal area (there’s a product out there called Snowballs—www.snowballsunderwear.com) or fanning air on the scrotal region, there’s no solid evidence at this time that these approaches significantly improve male fertility.
Heat Exposure at Work
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 other professions have significant heat exposure as well. Examples include chefs, bakers, ceramic oven operators, glassblowers, welders, and the crew of submarines, to name a few. The best intervention is letting the body’s natural cooling mechanisms work as efficiently as possible by wearing boxers or other loose underpants that allow the scrotum to stretch and increase the surface area for the evaporation of sweat.