Resting laptops on bare legs can lead to 'toasted skin syndrome', warn doctors
laptop for a few hours a day Damage can lead to skin cancers in some cases Temperature underneath computer can hit 52C Balancing your laptop on your knees could be bad for your skin, doctors have warned.
The heat generated by the ubiquitous devices can cause 'toasted skin syndrome' - a nettle sting-like rash that can cause permanent discolouration and, in rare cases, cancer.
Common in the days before central heating, when people huddled around open fires and electric heaters to stay warm, the condition is making a comeback in computer users.
Warning: A 12-year-old boy shows off the 'toasted skin' on his leg after using a laptop for several hours a day
In one recent case, a 12-year-old boy developed a sponge-patterned skin discolouration on his left thigh after playing computer games for a few hours every day for several months.
'He recognised that the laptop got hot on the left side; however, regardless of that, he did not change its position,' Swiss researchers wrote in the respected medical journal Pediatrics.
Another case involved an American law student with a mottled discolouration on her leg.
Her doctors was stumped until they learned the student spent about six hours a day working with her computer propped on her lap.
The temperature underneath the device reached 52c (125f) and, placed under the microscope, the affected skin resembled skin damaged by long-term sun exposure.
The case, from 2007, is one of 10 laptop-related cases reported in medical journals in the past six years, but many more are likely to have gone unrecorded.
Danger: People have been urged to use a heat shield under their laptop to protect their skin
Although the condition is usually harmless, it can cause permanent skin darkening.
And, in very rare cases, it can cause damage leading to skin cancers, said the Swiss researchers, Andreas Arnold and Peter Itin, of the University Hospital Basel.
'Toasted skin syndrome' can also affect bakers, silversmiths and others whose jobs involve being exposed to heat.
There are also reports of it being caused by prolonged use of heat pads to soothe sporting injuries.
Major computer manufacturers including Apple, Hewlett Packard and Dell warn in user manuals against placing laptops on laps or exposed skin for extended periods because of the burns risk.
The researchers advise anyone who is concerned about the syndrome to place their laptop carry case under the computer, to shield the body from the heat generated.
Other simple options include resting the machine on a desk or table.
This is not the first time the machines have been subject to a health alert, with warnings that frequent use could hamper male fertility.
Working with a laptop balanced on the thighs raises the temperature of sperm by up to 3C - enough to trigger fertility problems.
Dr Yefim Sheynkin, who led the research at the Sate University of New York and Stony Brook, warned that repeated warming over a period of years could cause irreversible damage.