What Could Rashes On Ear And Shoulders In Infants Indicate?

Hi, I have a 21 month old little boy, who has a rash that starts at his ears and goes down to his shoulders, it is also down his arms and in his armpits. He is not running a fever and the rash doesn't seem to be itchy to him. It just looks really bad. Does anyone have any idea what it is? He had something similar last June and the Dr. he goes to didn't know what it was but gave him an oral steroid that seem to clear it up, but this one is not as bad as it has been in the past.