Urticaria

Urticaria (from the Latin urtica, nettle, commonly referred to as hives, is a kind of skin rash notable for pale red, raised, itchy bumps. Hives are frequently caused by allergic reactions; however, there are many nonallergic causes. Most cases of hives lasting less than six weeks (acute urticaria) are the result of an allergic trigger. Chronic urticaria (hives lasting longer than six weeks) is rarely due to an allergy.

The majority of chronic hives cases have an unknown (idiopathic) cause. In perhaps as many as 30 to 40% of patients with chronic idiopathic urticaria, it is caused by an autoimmune reaction. Acute viral infection is another common cause of acute urticaria (viral exanthem). Less common causes of hives include friction, pressure, temperature extremes, exercise, and sunlight.