By Simon Handby on Tuesday, 26 February 2008
 Anyone who’s ever used a laptop computer will know that they can get
a little warm after just a few minutes. If you always work at a desk or
table, this may be all you ever notice, but if you use a laptop on your
lap, you could be outing your health at risk.
Sit with a very hot laptop on your thighs for any length of time and
you run the risk of more than just a crease in your trousers. In 2002,
a letter to The Lancet medical journal recounted the case of a 50-year old Swedish scientist
who had burned a rather intimate part of his anatomy after using his
laptop on his lap for an hour, apparently fully-clothed.
More worrying for men is that research has shown a strong link between raised temperature in the testes and a reduced sperm count. One study found that raising the average daytime temperature of the testes by one degree reduced sperm concentration by 40%.
For younger men, the consequences of a hot laptop could be altogether more long-lasting. In a study [paywall link] conducted at the State University of New York at Stony Brook, the scrotal temperature of 29 healthy volunteers was measured as they adopted a typical thighs-together laptop use position. Over the course of an hour, it was found to have risen by an average 2.1C. When the experiment was repeated with a working laptop, the average temperature increase was a further 0.7C.
Dr Yefim R Sheynkin, Associate Professor of Urology at Stony Brook, told us that “short-term non-repetitive increase in scrotal temperature is reversible”, but also warned that “frequent repetitive exposure to heat will not allow testicular function to recover properly and completely, which may put it at risk of permanent damage.”
If you can't stand the heat…
None of the components in a computer are specifically designed to produce heat, but many produce it as a by-product. It’s hard to make components that are totally energy efficient and so most of the wasted power ends up as heat. Some comes from obvious sources, such as the spindle motor of a hard disk drive, but the system processor and graphics chip are usually the worst culprits.
A desktop PC, with its large internal air spaces and powerful fans is easily able to keep itself cool, but the small dimensions of portable PCs make cooling a challenge. In a typical laptop, heat is conducted away from the processor by a heatsink, which is in turn cooled by a small fan.
Modern laptop processors run at around 50C, but this can rise to more than 90C if they’re working hard. If temperatures are allowed to rise unchecked, the processor risks burn out, so modern chips have thermal sensors and can throttle their speed if they get too hot.
Cooling a laptop effectively means more than just keeping each component at a suitable operating temperature, though. That heat has to go somewhere and if it isn’t properly dissipated, it can build up in parts of the laptop that come into contact with its user, such as the base, keyboard and wrist rest. The best laptop designs keep heat well away from these areas and in some models, heat is even conducted through the screen hinges and into the lid, where it can radiate away.
Cool it
 With these potentially serious side effects in mind, what can be done to reduce the heat that a laptop transfers to your lap? The simplest approach is to increase the separation between the two by always working at a desk or table. If you have no choice but work on your lap, put a specially designed laptop tray or at the very least, a thick magazine, between the laptop and your legs.
Even if you can't get away from the heat generated by your laptop, most come with software that can cool them down. Manufacturers normally bundle power management programs that let you set how hard various components work. These conserve battery power by reducing the clock speed of the processor and switching off components such as the hard disk after set periods of idle time, but such adjustments can also reduce heat output. Setting your processor to its lowest power, letting the hard disk spin down after just a couple of minutes and leaving the cooling fan on a medium or high setting could all reduce your laptop’s temperature.
As modern computers become faster and more powerful, manufacturers are being forced to consider heat from components which used to run comparatively cool. For example, rising memory bus speeds mean that SODIMM laptop memory can also generate a significant amount of heat. In an attempt to address this, Intel has developed memory modules with a thermal sensor that, like a processor, can throttle memory speed to conserve power and reduce heat.
Although there will doubtless be other innovations that help to cool laptops down, they'll have to keep pace with processors, memory and graphics systems that get ever more powerful. Though there's no definitive study linking hot laptops to fertility problems or ill health, a laptop that stays cool on the outside will always feel like a breath of fresh air.
How hot is your laptop?
These images from a thermal video camera show just how hot a laptop can get, and where. The first picture shows the laptop a few minutes after being brought into a warm room – it’s slightly darker than its surroundings as its still reaching ambient room temperature.
The second picture shows the same laptop after it has been running a demanding processor benchmark for several minutes (the colour of the surrounding area is has changed because the temperature scale has been changed to show the higher temperatures). Notice the hand in the third image – it’s much cooler than most of the laptop.
The hottest parts of this laptop (46.4C) appear are the top of the keyboard and middle of the wrist rest, beneath which sit the processor and its cooling apparatus sit. The base of the screen is also quite warm – this is where its controlling electronics are housed. The hand at the bottom right of the image is at body temperature, so you can see how much hotter the laptop is.
Flip the laptop over and temperatures are higher still. The white hotspot corresponds to that seen on the keyboard but here, temperatures reach a painful 50C. Leave this laptop resting bare flesh for more than a few minutes and it could result in a serious burn.
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