Uticaria (Hives), Acute

Presentation

The patient is generally very uncomfortable with intense itching. There may be a history of similar episodes and perhaps a known precipitating agent (bee or fire ant sting, food, or drug). More often, the patient will have only a rash. Sometimes this is accompanied by nonpitting edematous swelling of the lips, face, hands, and/or genitalia (angioedema). In the more severe cases, patients may have associated abdominal pain and vomiting (especially if an offending allergen was ingested), wheezing, laryngeal edema, and/or frank cardiovascular collapse (anaphylaxis).

Lesions may occur anywhere on the body. The urticarial rash consists of sharply defined, slightly raised wheals surrounded by erythema and tends to be circular or appear as incomplete rings ( Figs. 185.1, 185.2, 185.3 , and 185.4 ). Each eruption is transient, lasting no more than 8 to 12 hours, but may be replaced by new lesions in different locations. It is not unusual to see these characteristic wheals appear or disappear from areas on the patient’s body, even during a brief encounter. The edematous central area can be pale in comparison with the erythematous surrounding area. These eruptions may occur immediately after exposure to an allergen, or they may be delayed for several days. Allergic reactions to foods or medications are self-limited, typically 1 to 3 days, but will recur with repetitive exposures to cross-reactive substances. Urticaria can sometimes last for 1 to 3 weeks with some drug reactions.

Contact urticaria (in which contact of the skin with an allergen, such as latex, causes hives at the site of contact) may be complicated by angioedema and even severe anaphylaxis (see Chapter 162 ).