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Hereditary and Acquired Angioedema

(Acquired C1 Inhibitor Deficiency)

By Peter J. Delves, PhD

Hereditary angioedema (a genetic disorder) and acquired angioedema (acquired C1 inhibitor deficiency) are caused by a deficiency or malfunction of C1 inhibitor, which is part of the immune system. Both disorders result in repeated episodes of swelling under the skin.

Hereditary angioedema and acquired angioedema resemble angioedema caused by an allergic reaction, with swelling of areas of tissues under the skin. However, hives do not develop and the cause is different.

Hereditary angioedema is a genetic disorder that causes a deficiency or malfunction of C1 inhibitor. C1 inhibitor is one of the proteins in the complement system, which is part of the immune system. Symptoms usually start during childhood or adolescence.

Acquired angioedema , a rare disorder, differs from hereditary angioedema. It develops when certain cancers (such as lymphoma) or autoimmune disorders (such as systemic lupus erythematosus [lupus] or dermatomyositis) cause a deficiency of C1 inhibitor. Symptoms usually start later in life, after people have developed a disorder that can cause this deficiency.

In both hereditary and acquired angioedema, swelling (angioedema) may be triggered by

  • A minor injury, as may occur during a dental procedure

  • A viral infection

  • Certain foods

  • Pregnancy

  • Exposure to cold

Stress, such as that due to anticipating or having a dental or surgical procedure, can make angioedema worse.


The face, lips, tongue, hands, feet, genitals, and/or other areas of the body may swell, as may the membranes lining the mouth, throat, airways, and digestive tract. Typically, the swollen areas are slightly painful, not itchy. Hives do not appear. Nausea, vomiting, and cramps are common.

Swelling in the voice box (larynx), throat, or tongue can interfere with breathing.


  • Blood tests

Doctors suspect hereditary or acquired angioedema if both of the following are present:

  • People have swelling in the face, lips, tongue, hands, feet, genitals, and/or other areas of the body but do not have hives.

  • The swelling recurs, and no cause is apparent.

If family members also have these symptoms, doctors suspect hereditary angioedema.

Doctors diagnose hereditary or acquired angioedema by measuring C1 inhibitor levels or activity in a sample of blood.


  • Drugs such as ecallantide or purified C1 inhibitor

  • Fresh frozen plasma

  • Drugs to prevent future attacks

Certain drugs, such as ecallantide or purified C1 inhibitor (which is derived from human blood), can sometimes relieve the swelling. However, these drugs are not always available. In such cases, fresh frozen plasma may be given. Antihistamines and corticosteroids are not effective.

Pain relievers, drugs to relieve nausea (antiemetic drugs), and fluids may help relieve symptoms.

Emergency treatment

Sometimes if the airway suddenly swells and people have difficulty breathing, doctors must open the airway. To do so, they may inject epinephrine under the skin or into the muscle to reduce the swelling. However, epinephrine may not reduce the swelling quickly or long enough. Then doctors insert a breathing tube in the windpipe through the person’s mouth or nose (intubation).

Sometimes doctors have to make a small incision in the skin over the windpipe (trachea) to insert the breathing tube.

Drugs to prevent attacks

Stanozolol and danazol (which are synthetic male hormones) may help prevent subsequent attacks. These drugs may be given for a few days before and after a dental or surgical procedure, which may trigger an attack. Or they may be given to prevent attacks over the long term.

These drugs, taken by mouth, can stimulate the body to produce more C1 inhibitor, but they may be less effective for acquired angioedema.

Because these drugs can have masculinizing side effects, the dose is reduced as soon and as much as possible when these drugs are given to women for a long time.

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