A. He could have cold induced urticaria, a form of hives that is triggered by being exposed to cold temperatures or a rapid change in temperature.
Does he get swelling of his hand after holding something cold?
Is it even worse after he comes inside and gets warmed up?
You should also make sure that it is really the exposure to cold weather that is the trigger for this reaction. For example, you might be fooled if he was allergic to peanuts and eat a peanut butter and jelly sandwich each morning for breakfast before going outside. In this case, it might be the peanuts and not the cold weather that triggered the rash and swelling.
In addition to foods and medicines, many other things can trigger hives or urticaria, including allergic and non-allergic triggers. These include exercise, stress, infections, and insect stings.
An allergist should be able to help sort out what is triggering his reaction.
An ice cube test, under close observation of your doctor, might also be able to tell if really has cold induced urticaria. With an ice cube test, the ice cube is held on a person's forearm for about 4 minutes and then the area is watched to see if it becomes itchy and swollen.
Treatment of cold induced urticaria include trying to avoid things that trigger the reaction, such as not swimming or bathing in cold water and wearing warm clothing. An antihistamine, like Zyrtec, might also be helpful. An epinephrine pen might also be helpful in case he has a more serious reaction.
Fortunately, cold induced urticaria often goes away eventually, although it may take months or years.