If you've ever felt your legs heating up while working with your laptop on your lap, you're not alone. It can actually lead to something called "toasted skin syndrome." It's a strange-looking mottled skin condition caused by long-term heat exposure. Read more about it here.

In one recent case, a 12-year-old boy developed a sponge-patterned skin discoloration on his left thigh after playing computer games. But he was doing it several hours a day for many months.

"He recognized that the laptop got hot on the left side; however, regardless of that, he did not change its position," Swiss researchers reported in an article published Monday in the journal Pediatrics.

And he isn't the only one. Another case involves a Virginia law student who developed the mottled discoloration on her leg. The doctor who her was stumped until she learned the student spent about six hours a day working with her computer propped on her lap. The temperature underneath registered 125 degrees.

These are among 10 laptop-related cases reported in medical journals in the past six years.

The condition also can be caused by overuse of heating pads and other heat sources that usually aren't hot enough to cause burns.

It's generally harmless but can cause permanent skin darkening. In very rare cases, it can cause damage leading to skin cancers, researchers say.

They do not cite any skin cancer cases linked to laptop use, but suggest, to be safe, placing a carrying case or other heat shield under the laptop if you have to hold it in your lap.

Major manufacturers like Apple, Hewlett Packard and Dell warn in user manuals against placing laptops on laps or exposed skin for extended periods of time because of the risk for burns.

Dell, for example, sells a laptop pad for $24.99. It promises to "raise the back edge of your laptop to increase airflow - improving the cooling efficiency of your laptop."

And listen to this: a medical report several years ago finds men who used laptops on their laps had elevated scrotum temperatures. If prolonged, that kind of heat can decrease sperm production, which can potentially lead to infertility. Whether laptop use itself can cause that kind of harm hasn't been confirmed.

In the past, "toasted skin syndrome" has turned up in workers whose jobs require being close to a heat source, including bakers and glass blowers, and, before central heating, in people who huddled near potbellied stoves to stay warm.

A doctor at Children's Memorial Hospital in Chicago says chronic, prolonged skin inflammation can potentially increase chances for squamous cell skin cancer, which is more aggressive than the most common skin cancer. But it's unlikely computer use would lead to cancer since it's so easy to avoid prolonged close skin contact with laptops.

Information from the Associated Press was used in this article.