I have the same condition and it is a form of hives called Cold Utricia. Your body is allergic to the cold once your body has been warmed. There really isn't a ryhme or reason why this happens as far as doctors are concerned. I have been to several doctors (allegerists, dermatologist) and my Internal Medicine doctor was the one who made the diagnosis. I'm currently on Hydroxine, Zrytec and Ritadine 2x a day. I'm further exploring other options until I find relief. As you stated, the itch dosen't happen all the time, but when it does happen it is enough to drive you nuts. I hope you and your sister continue to search for an answer....please don't ignore it. God Bless you both.