What Could Be The Itchy Red Blisters On Leg?

I have had a small itchy circular area (about 1/2 dime size) on the outside of my lower leg for a few weeks. There was a tiny blister at first that broke w/ the scratching. It is slightly raised, and has white dry skin in the middle of the circle, surrounded by a light red. It still itches. Any ideas what it could be???