First of all i would like to tell you that Skin Rash is not any particular disease, it means only the changing in skin or rashes from which someone feels difference in skin, so doctors and experts do not call it any disease like Mesothelioma or Diarrhea etc.
Rashes are not dangerous to human being else they take position of chickenpox or allergic spots.
There are many types of rashes and they have their treatment according to their conditions.
Some of them are Allergic Drug Rash, Viral Rash, Bacterial Rash, Hives, Lime Rash etc.
Their care is must and one should not itch on the infected part.