Urticaria (or hives) are a kind of skin rash notable for dark red, raised, itchy bumps. Hives are frequently caused by allergic reactions, however there are many non-allergic causes. For example, most cases of hives lasting less than 6 weeks (acute urticaria) are the result of an allergic trigger. Chronic urticaria (hives lasting longer than 6 weeks) are rarely due to an allergy. The majority of patients with chronic hives have an unknown (idiopathic) cause.
