An itchy rash is an inflammatory reaction of the skin. An itchy rash is a symptom of a wide variety of mild to serious diseases, disorders and conditions.Itchy rashes differ in severity, frequency and duration depending on the underlying cause.Itchy rashes can appear as blotchy or tiny spots or occur in a large, solid continuous area.n itchy rash is an inflammatory reaction of the skin. An itchy rash is a symptom of a wide variety of mild to serious diseases, disorders and conditions.