I've also had problems with chronic hives as well as dermatographism. After eliminating all of the skincare/detergents, I ended up tracking my food intake and narrowed it down to a few culprits. The big one that I can almost prove is food colorings, especially FD&C Yellow #5. Others I'm not sure about are preservatives like sodium benzoate, etc. It was really hard to tell because I wouldn't get anything immediately after eating. It took days of a dose accumulating in my body, and then another external trigger like stress, menstruation, heat/pressure/friction, or being sick with the cold/flu.

Now that I've figured out the foods, I still occasionally get periods where I get lots of hives and it's usually something I've eaten (say at a restaurant or free food at work, god I need to learn to say no!) or because I'm sick.