It's been a joke among computer users that working too long with a notebook PC on your lap can lead to a laptop tan. Swedish researchers aren't laughing. They say using a hot laptop that rests on your legs can give you mottled, discoloured skin that could lead to a condition called "toasted skin syndrome".

The condition known as toasted skin syndrome was linked to laptop use by the researchers in an article appearing in the October issue of Pediatrics. In a case cited by the journal, a 12 year old boy developed "sponge-patterned skin coloration" on his left thigh after playing video games with the computer on his lap for a few hours a day for several months. The image above, courtesy of Dr. Benabio, of a "toasted" thigh shows the disgusting details.

Another case that's come to light involves a law student in Virginia, the AP reported. In that instance, the future lawyer showed up at the Eastern Virginia Medical School complaining about mottled discoloration on her leg. When probed about her work habits, the student revealed she spent about six hours a day working with her laptop which could reach a temperature of 125 degrees Fahrenheit, according to the assistant dermatology professor who examined the student, Dr. Kimberley Salkey.

The Swiss researchers, Drs. Andrea Arnold and Peter Itin, told the AP that laptops rarely get hot enough to burn their operators, but they can cause skin damage that might lead to cancer. The physicians, however, could not cite any specific cases where that happened.

Other dangers from prolonged laptop usage in a lap have been reported in the past, according to the Daily Mail. For example, Dr. Yefim Sheynkin conducted research at New York State University demonstrating that a laptop balanced on the thighs raises the temperature of male sperm by three degrees Centigrade. That could trigger fertility problems and over time could cause irreversible damage, he concluded.