Urticaria (hives)

Urticaria, or hives, is a skin reaction in which raised, itchy welts (weals) appear, often pink or pale with a red flare, and characteristically move around and fade within hours only to appear elsewhere. It is caused by the release of histamine from mast cells in the skin. Sometimes it comes with deeper swelling of the lips, eyelids or hands (angioedema). It is divided by duration. Acute urticaria (less than six weeks) is very common and often follows a viral infection, a food or drug reaction, or an insect sting, and usually settles on its own. Chronic urticaria (more than six weeks, most days) is, perhaps surprisingly, usually not due to an allergy at all — in most cases no external cause is found (it is often autoimmune), and extensive allergy testing is unrewarding. Some forms are triggered physically, by pressure, cold, heat, or exercise. It is generally not dangerous, though it can be very distressing, and responds well to antihistamines.

• Diagnosis is clinical — from the typical fleeting, itchy weals; blood tests are usually not needed, especially for acute hives.
• For chronic urticaria — a limited screen (such as full blood count, CRP/ESR, thyroid function) looks for a rare underlying cause; extensive testing is discouraged.
• Total IgE, eosinophils — may be checked but are non-specific.
• Allergen-specific IgE — only if the history clearly points to a specific allergic trigger.
• Thyroid antibodies — chronic urticaria has an association with autoimmune thyroid disease.

• Raised, itchy welts (weals) that appear and fade, often within hours
• Welts that move around the body and vary in size and shape
• Itching, sometimes intense
• Deeper swelling of the lips, eyelids or hands (angioedema) in some people
• Individual welts lasting less than 24 hours (longer suggests a different diagnosis)
• Acute (under 6 weeks) or chronic (over 6 weeks, most days)