If I understand your comment urticaria is a skin rash with red, rash, with raised itchy bumps, known as hives. In my case usually with angioedema (swelling) of the lips, mouth, cheeks, tongue, face. I have a long history of chemical, environmental and food allergies. Change to probiotic diet helped me the best. My last food allergy blood and skin prick tests were negative and now appears that its gut bacteria related. We are now looking at mast cell disease (mastocytosis) which has similar similarities to food allergies. We are considering starting on a low histamine diet. Presently I ingest probiotics that are high in histamines. I take multiple antihistamines for chronic sinus, asthma, urticaria and angioedema.
The doctors test for triggers. They usually start with skin prick tests, blood tests (RAST) and then a oral food challenge. Avoidance is the best solution once triggers are identified.

Hi, I have HAE and have suffered with urticaria in the past. Best thing i ever did was follow a salicylate free diet. Does amazing things for so many symptoms. I still have edema but very seldom urticaria.