Yesterday I read posts on PR about cold urticaria, an allergy to cold temperatures. It was the first I had heard of it. Then today I heard an item on Australia's Radio National about cold urticaria. http://www.abc.net.au/radionational/programs/healthreport/allergic-to-the-cold/7554512 You can listen to the 8 minute item or read the transcript. In sufferers, mast cells release histamines and other chemicals on exposure to cold. This can cause itchy hives and even full-on anaphylactic reactions. The mechanism is not well understood. Cold urticaria can be inherited. But what I really found interesting was that ongoing cold urticaria can be triggered by an 'infection such as glandular fever or a bacterial stomach ulcer'. (Discussed around the 5 minute mark). It's the first time, I think, I have heard of an allergy being triggered by an infection. Also, the item says that sometimes treating the underlying infection can eliminate the cold urticaria.