These swellings arise suddenly, rarely persist longer than a day or two, and may recur indefinitely. Urticaria is a common and bothersome skin disorder that responds poorly to skin medications. More than one-fifth of the population has suffered an eruption at some time in their lives. Urticaria has many causes, both immunologic and non-immunologic. In a very small number of cases, hives may be the symptom of a more serious underlying disease.
Some cases apparently result from an allergic response, such as to certain drugs and foods.
Seasonal hives in people suffering from asthma, hay fever or eczema also presumably result from an IgE-mediated allergic reaction. Why some people should react with hives to allergens that usually cause respiratory symptoms remains unknown. These cases do not involve immunologic reactions, but may stem from an interference with an enzyme called prostaglandin synthetase. Another mechanism is involved in hereditary angioedema , a potentially fatal inherited disease that produces episodic swelling of the face and extremities. In addition, swelling may occur in the tongue, throat, or larynx, shutting off air to the lungs.