A couple of days ago I developed a horrid rash on my arms, legs and stomach. I used Benadryl and Hydrocortizone but it did not help. Today I went to the Derm who said it was an allergic reaction, prob. to the Naproxin I started taking a week ago for a shoulder problem. He gave me a script for Prednisone and I took it about 4 hours ago. Now my rash/itch is spreading to my hanRAB and feet. It is so itchy. I took another Benadryl it's not helping. I stopped with the Naproxin yesterday am, so why is this rash still developing? Does it have a run a full course through my body? Why doesn't it just stop?