Hives, or urticaria, are raised, swollen, reddened, itchy areas of skin known as wheals or welts. Hives often occur in response to a physical trigger, and appear and disappear quickly, sometimes moving from one area of the body to another over several days. Fluid leaking from small blood vessels causes swelling, pediatrician and columnist Alan Greene explains. Release of histamine from cells often causes the fluid leakage. Angioedema, a deeper swelling, often affects the face. Several factors can trigger hives, which usually are self-limiting, but can cause serious reactions.

Allergies

Allergic hives and facial swelling can occur when a person encounters a substance, called an allergen, to which she has developed sensitivity. Exposure to an allergen, such as a food, plant or medication, sets off a reaction that can produce hives or angioedema 1. Some allergic reactions are very common. A large percentage of people, for example, have an allergy to poison ivy. Animal dander and saliva, pollen, insect stings, molds and dust mites often trigger hives or angioedema 1. Common food allergies include peanuts, shellfish, milk, chocolate and eggs. Food additives, such as sulfites and salicylates, also can cause hives and swelling.

Common medication allergies that cause hives include penicillin and other antibiotics, aspirin and blood pressure medications, but any drug can cause hives, MayoClinic.com warns 13.

Antibody Production

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Antibodies produced in response to illness, blood transfusions and certain thyroid problems can trigger an outbreak of hives and angioedema in some people, according to the Mayo Clinic 1.

Hereditary Angioedema

Hereditary angioedema, an inherited immune problem caused by low levels of a protein called the C1 inhibitor, causes facial and airway swelling, MedlinePlus reports 2. Surgery, sickness or dental procedures may trigger swelling, which can develop quickly in the face, throat and intestines. Nausea, vomiting and cramps may accompany an attack, according to the Merck Manuals. The swelling of hereditary angioedema is painful rather than itchy, and hives are not visible 12. Hereditary angioedema is difficult to treat, and can cause death 2. Epinephrine helps reduce swelling in severe cases. C1 inhibitor concentrate helps reduce swelling, if available.

Physical Factors

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Environmental factors can cause hives and facial swelling in susceptible people. The most common type of reaction, cold urticaria, occurs in response to cold air or water, pediatrician Greene says. Solar urticaria occurs in response to sun exposure, while cholinergic urticaria occurs after exercise, heat exposure or stress. Water or sweat triggers aquagenic urticaria, while dermatographia appears in about 5 percent of people after something firmly strokes or scratches the skin.