Most of the time urticaria (hives) and angioedema (deep swellings under the skin) are manifestations of an allergic reaction triggered by medications, foods, infections, certain physical agents like heat, cold, water, sun, other allergens and systemic illnesses. Chronic urticaria is defined as urticaria that persists past six weeks in duration. Much less often chronic urticaria is caused by an autoimmune disease, that affects mast cells.  These cells are the ones that release histamine that triggers formation of hives. So the first thing in treatment of chronic urticaria is diagnosis.  The diagnostic work-up includes blood tests, urine, stool to check for parasites, and x-rays of the chest, sinuses and teeth.  A prick or scratch test to test for airborn or food allergens is also in order. If nothing is found on the workup, then the relief is mostly symptomatic with antihistamines.