What Causes Redness And Dryness On Skin Of Knuckles And Back Of Thumb?

every spring, this time of year, my hands get irritated by something. they start out by getting red especially on the knuckles and the back of my thumbs. eventually they turn to small blisters. and finally the skin becomes very dry and cracked. this process takes several weeks. I think if it was poison, I d get it on other parts of my skin, but I don t.