What are hives and angioedema?

Most people recognize hives - those sudden instances of swelling of the skin that usually itch, burn, or sting. Less familiar, however, is the condition's close cousin, angioedema, a similar kind of swelling of the deeper tissues beneath the skin.

Hives and angioedema are related because they are similar reactions to the same basic cause, a release in the skin of chemicals including called histamine. In most cases, histamine is and these other chemicals are a byproduct of the body’s specialized mast cells as they go about their job of destroying allergens, which are any substances that cause allergic reactions. Fighting allergens is not the only way that histamine is produced, however. Irritation caused by sunlight, some medications, and unknown sources can make mast cells release histamine, too.

Whatever the reason for its release, histamine produces hives and angioedema by dilating the small blood vessels in the skin and causing fluid to leak from them. This in turn generates swelling. It also can stimulate gastric acid secretion and cause certain smooth muscles to contract.

Hives—or more technically, urticaria—are pale red welts that can appear anywhere on the body in splotches as small as a pencil eraser and as large as a dinner plate. These splotches sometimes join together to form larger areas known as plaques. Whether large or small, hives and plaques often fade within a few hours, but can last up to a day or longer.

In general, angioedema lasts longer than urticaria, but the swelling usually goes away within 24 hours. Symptoms include deep swelling around the eyes and lips, and sometimes swelling of the genitals, hands, and feet. Occasionally, severe and prolonged swelling of the tissue can be disfiguring. In rare instances, angioedema of the throat, tongue, or lungs can block the airways, making breathing difficult and potentially endangering the life of the victim.

Types of urticaria and angioedema

Doctors usually classify hives and angioedema according to the following categories:

  • Acute urticaria is a case of hives that lasts less than 6 weeks. The most common causes are foods, medications, latex, or infections, but insect bites and internal disease can be responsible too. The most common foods that trigger hives are nuts, fish, tomatoes, and fresh berries. Medications that can cause hives and angioedema include aspirin, other nonsteroidal anti-inflammatory medications such as ibuprofen, high-blood-pressure medications (ACE inhibitors), and painkillers such as codeine.
  • Chronic urticaria and angioedema lasts more than 6 weeks. The cause of this type of reaction tends to be much more difficult to identify than the cause of the acute kind. For this reason, it is often not found. In fact, the cause of chronic urticaria remains unknown in more than 80% of cases.
  • Physical urticaria is a case of hives caused by direct physical stimulation of the skin from exposure to cold, heat, sun, vibration, pressure, sweating, exercise, and other sources. These hives usually occur at the site of the stimulation and rarely appear elsewhere. Most of outbreaks in this class appear within 1 hour after exposure.