What Causes Red And Itchy Patches On Skin In Summers?

A few years ago, while working outdoors on a sunny day during the summer, I managed to get my arms seriously burnt by the sun. In a few places I had swelling from where fluids had collected. I treated myself with aftersun cream and everything was good in a few days. However since then, and usually only at the beginning of the summer, I get red spots or patches where my skin flares up and feels itchy. Aftersun or such soothing creams help. After a month the patches disappear and I don t have any further problems. Its almost as if my body has a memory of the original burns an remembers when it sees the early summer sun; but as time passes it acclimatizes to the summer and stops reacting to the sun! Any thoughts on that?? Thanks