How the heat from a laptop can 'toast' the skin on your thighs

• Toasted' boy used 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 cause permanent discolouration of the skin and, in rare cases, cancer, doctors have warned.

The heat generated by the computers can cause a nettle sting-like rash - a condition named 'toasted skin syndrome'.

Common in the days before central heating, when people huddled around fires and electric heaters to stay warm, it is making a comeback in the laptop generation...

      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 medical-journal Pediatrics. 

Another case involved an American law student with a mottled discolouration on her leg.

Her doctors were stumped until they learned she spent about six hours a day working with her computer propped on her lap.

The temperature underneath the device reached 52c and, placed under the microscope, the affected skin resembled skin damaged by long-term sun exposure. 

The case, from 2007, is one of ten laptop-related incidents reported in medical journals in the past six years, but many more are likely to have gone unrecorded...

               Danger: Balancing a laptop on bare legs can can cause permanent skin darkening..

Although the condition is usually harmless, it can cause permanent skin darkening.

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.

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 risk of burns.

The researchers warned that children's skin is particularly susceptible to heat.

But Dr Bav Shergill, a consultant dermatologist and spokesman for the British Association of Dermatologists, urged people not to worry.

He said: 'It usually resolves itself without any permanent skin discolouration."