Angioedema is a swelling similar to hives, but the swelling is beneath the skin rather than on the surface. The swellings are called welts.

See also: Hereditary angioedema

Angioedema may be caused by an allergic reaction. It is associated with the release of histamine and other chemicals into the bloodstream. The body releases histamine when the immune system detects a foreign substance called an allergen.

Sometimes the cause of angioedema is never found.

The following items may cause angioedema.

• Animal dander (scales of shed skin)
• Certain medications (drug allergy)
• Emotional stress
• Exposure to water, sunlight, cold or heat
• Foods (such as berries, shellfish, fish, nuts, eggs, milk, and others)
• Insect bites
• Pollen

Hives and angioedema may also occur after infections or illness (including autoimmune disorders, and leukemia).

There is a form of angioedema that runs in families and has different triggers, complications, and treatments. This is called hereditary angioedema, and is not discussed here.

The main symptom is the sudden development of red welts. The welts usually occur around the eyes and lips. They may also be found on the hands, feet, and throat.

The welts are painful and may be itchy. They turn pale and swell if irritated.

Other symptoms may include:

• Abdominal cramping
• Breathing difficulty
• Swollen eyes and mouth
• Swollen lining of the eyes (chemosis)

The doctor will look at your skin and ask you if you have been exposed to any irritating substances. A physical exam might show stridor (crowing sound when inhaling) if the throat is affected.

Rarely, allergy testing may be performed.