MY 12 year old son scraped his elbow while roller blading. He didn't tell me about the injury for aprox. three days. When I first saw the wound it was black and crusty. I put a antibiotic cream and bandage. The next day it looked good and was pinkish looking. He has very little pain. Tonight the wound still looks good but small pimples or blisters are running up his arm close to the wound. Are the pimples a sign of stafh infection, or any thing I should worry about?