My Hands, Arms, Sometimes My Legs Get Very Itchy. Especially

My hands, arms, sometimes my legs get very itchy. Especially on my hands, the itch turns into a blister that I absolutely have to scratch. When the blister opens, I finally get relief from the itch, but within a day or so I have a scab where the blister was and it takes days to heal. I herd that it could be a type of psoriasis. Do you know what this might be?