Urticaria, commonly referred to as hives, is a reaction of cutaneous blood vessels that produces a transient dermal edema consisting of papules or plaques in different shapes and sizes.
Angioedema refers to edema that is deeper than urticaria that involves the dermis and subcutaneous tissue.
A total of 10% to 20% of the population has at least one episode of urticaria or angioedema at some point in his or her lifetime.
Mast cell activation causes degranulation of intracellular vesicles that contain histamine, leukotriene C4, prostaglandin D2, and other chemotactic mediators that recruit eosinophils and neutrophils into the dermis.
Histamine and chemokine release lead to extravasation of fluid into the dermis (edema). Histamine effects account for many of the clinical and histologic findings of urticaria.
As with drug reactions, urticaria may be immune-mediated or nonimmune-mediated (see discussion in Chapter 26: Adverse Cutaneous Drug Eruptions).
Causes of urticaria and angioedema include the following:
Immunologic: mediated by immunoglobulin E (IgE) includes food, drugs, and parasites.
Complement-mediated: includes serum sickness and whole blood transfusions.
Physical stimuli: non-IgE-mediated includes cold, sunlight, and pressure (e.g., dermatographism).
Occult infections: sinusitis, dental abscesses, and tinea pedis.