Varicella rash: Varicella (chickenpox) is characterized by a rash, often the first sign of the disease. The rash of chickenpox develops in crops with raised red spots arriving first, progressing to blisters that burst, creating open sores, before crusting over. This process usually starts on the scalp, then the trunk (its area of greatest concentration), and finally the arms and legs. Any area of skin that is irritated (by diaper rash, eczema, sunburn, etc.) is likely to be hard hit by the rash. The rash is typically very itchy (pruritic).