Recurring Swollen And Itchy Rashes In Extremities Of Body, Bright Red Gradually Turning Brownish. Possible Causes ?

Hi, I wanted to know what kind of condition(s) could I possibly have. I randomly have a recurring condition where an area of my body develop some kind of rash. It is raised and itchy and swollen. Sometimes it s large, and sometimes it s small patch of the affected skin. The rash doesn t go away quickly, rather it stays bright red after a few weeks. It gradually became flat and not swollen anymore and then the rash gradually turn brownish and it is difficult to fade or disappear. The rashes only appear on my extremities, arms and legs, so far.