You an diagnose the rash by What it looks like or alternatively by Where the rash is found on the body.
What the rash looks like.
Red and scaly - Scale is white material on the surface when you scratch it.
Red and No Scale Can be flat (macular) or raised (papular or nodular)
Pustules - Yellow fluid filled small blisters
Vesicular or Blisters - Clear fluid filled small blisters
Rash is a Funny Shape, Colour Texture or Distribution on the body
Where is the rash on the body