The itching and hives result from increased levels of histamine, which is released by mast cells in the skin. Many different factors can cause the increase in histamine levels. Many people believe urticaria is an allergic disease; however, fewer than 10 percent of urticaria cases are the result of an allergic reaction.

There are dozens of causes of and triggers of chronic urticaria. Most causes fall into one of three groups:

1. Sensitivity to food additives (colorings, aromas, or preservatives) or to medications
2. Chronic infections, for instance in the digestive tract; these do not necessarily lead to further health problems apart from urticaria.
3. Auto-immune reaction: This means that the immune system is attacking the body’s own tissues, resulting in hives.

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