Hives, also called urticaria, nettle rash or welts is essentially an allergic skin rash.
Hives typically manifest as raised, red and severely itchy bumps that may be limited to one part of the body or form an almost whole body rash. In most cases, the rash resolves within a few days and acute urticaria usually resolves completely within six weeks. Rashes that persists for over six weeks are termed chronic urticaria.
Hives usually manifest when a person is exposed to a substance that triggers the release of chemical messengers such as histamine from cells in the skin. Histamine causes surface blood vessels to dilate, leading to redness and also leakage of fluid and chemicals from the vessels that cause swelling and itching of tissue.
Diagnosis and treatment
Hives are mainly caused by an allergic reaction to certain substances or chemicals that a person has come into contact with and identifying these is most important. Hives are mostly diagnosed on clinical examination of the lesions and obtaining a detailed history of allergic symptoms that occur after the intake of any particular foods, inhalation of dust, contact with animal hair, or on seasonal exposure to pollen for example. Diagnosis is confirmed by certain tests such as the skin prick test, the patch test or the radio-allergosorbent tests (RAST test).
Most cases of urticaria resolve without treatment, with the rash healing on its own within a few days. However, scratching of the itchy hives may damage the surface of the skin and possibly lead to secondary skin infections, further complicating the condition. However, antihistamines can be used to relieve this itching and are usually available over the counter at pharmacies. Long term cases or particularly severe cases of hives may require the use of oral or locally applied medications.
Reviewed by Sally Robertson, BSc