OK. Three cases.
Mine was chronic urticaria. 8 years of it. First it was caused by saccharin. Then aspartame, then it was just constant and we couldn't figure it out. 8 years it was partially suppressed by a combination of Singulair in the morning and Zyrtec in the evenings (I was under the care of a doctor). It was only after we found out about my children, that I learned what was causing mine - I had food sensitivities to gluten, cow dairy, eggs, and to a smaller extent, soy.
My younger daughter, on the other hand had cholinergic urticaria - a completely different type of hives, but also brain symptoms (see http://www.ItsNotMental.com ) and was even on heavy-duty psych meds for most of her childhood. Her hives and allergies and later on asthma as well were partially suppressed with 4 meds - Singulair and BOTH Zyrtec and Allegra, plus an emergency inhaler. COLD helped subdue her outbreaks of her type of hives, and any increase in body temperature caused worsening.
Again - food allergies/sensitivities were problematic for her and she was found to have a problem with gluten (Celiac), cow casein, egg whites, soy. She turned out to be severely not absorbing some nutrients.
I was upset with our allergist who was NOT the one who found this. He had only given an IgE allergy testing. Had never told us about IgG and IgA testing, or even a suggestion to try gluten-free to see if that helps. Gluten intolerance is increasing globally.
Third case is my niece. Hers was simple. She was allergic to the laundry detergent and we switched back to the hypoallergenic kind used for babies (like Dreft).