Pityriasis rosea hit top of back of the legs of a girlfriend of mine n burns like skin is cracking open ? what to do, think ..

Sure of diagnosis: Pityriasis rosea is a self limiting disease. Usually there is an initial patch on chest or back called the herald patch. It is mostly spread diffusely on back and chest. If you look at the back at a distance you can see a x-mas tree pattern. It can be itchy. Unless severe it usually does not crack. Best way to diagnose it is to look at it.