It is better to keep your laptop off your lap, according to a case report published in the US journal Pediatrics.
Excessive use of notebooks, especially if faulty or badly-designed, can cause "toasted-skin syndrome" or permanent upper leg heat damage, doctors said.
The report from Andreas Arnold and Peter Itin, from Basel University Hospital's dermatology department, described how a 12-year old boy suffered skin discolouration on his left thigh caused by overuse of a laptop.
This kind of scorching has also been observed on people exposed to heating pads or hot water bottles for prolonged periods of time.
The condition, called "erythema ab igne", was also common throughout the industrial revolution in workers who were exposed to ovens or furnaces for long periods.
The Swiss doctors specified this was the latest of 10 cases reported worldwide.
Earlier this year, Argentine researchers claimed Wi-Fi radiation from a laptop could affect male fertility by reducing sperm motility and fragmenting DNA.
Similar research in 2004 suggested heat from a laptop could have a "considerable negative effect on spermatogenesis and fertility" for men.
Many computer manuals now carry a warning that laptops should not be rested on the upper thighs.
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