Have you ever worked on your laptop computer with it sitting on your lap, heating up your legs? If so, you might want to rethink that habit. Doing it a lot can lead to “toasted skin syndrome,” an unusual-looking mottled skin condition caused by long-term heat exposure, according to medical reports.

In one recent case, a 12-year-old boy developed a sponge-patterned skin discoloration on his left thigh after playing computer games a few hours every day for several 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.

Another case involved a Virginia law student who sought treatment for the mottled discoloration on her leg.

Dr. Kimberley Salkey, who treated the young woman, 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.

That case, from 2007, is one of 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. Read more in North Jersey.