To the PP whose son is having issues:
I had a major issue with hives a few years back. The doctor explained that my histamines were in overdrive because of "something" I was in contact with. Once your histamines are worked up, anything can set your skin off - cold, heat (like getting warm while sleeping), perfumes you have used previously without incident, brushing up against something, rough fabric, anything.
The way the doctor "proved" her case was to lift my shirt in the back and "write" an X on by back. Within a minute or two I started to itch all over my back, and the little red lines she had drawn were two inch wide, inflamed red marks. Because my histamines were in overdrive, it made it pretty hard to discover what the allergy was because I would react to everything, even products I had used for years.
On her advice, I eliminated ALL perfumes and dyes in everything I used around the house or on by body. Wore gloves to clean. Watched and charted my diet. Charted my breakouts.
It took a LONG time, but I finally came to the conclusion that it was my Nair that I used in place of shaving. I had used Nair for years so I don't know if the company changed an ingredient or a perfume or what, but I haven't had hives since. Well, I also have stuck with the perfume and dye free detergent and use the dryer balls rather than fabric sheets. And still wear gloves to clean with harsh chemicals. (I'm still a little nervous it will come back, so I take precautions. Hives are miserable.)
For the OP, I feel for you. I have heard of an allergy to cold (or maybe it was just sudden temp changes, not the cold itself? I believe someone said that getting chilled swimming sets their off.). Is that what causes yours, do you think?? Do you get them at any other time or just with the cold? That would be miserable around here. I think I'd have to move.

Hated, hated, hated the hives.