(See also Overview of Allergic Reactions Overview of Allergic Reactions Allergic reactions (hypersensitivity reactions) are inappropriate responses of the immune system to a normally harmless substance. Usually, allergies make people sneeze; the eyes water and itch... read more 
.)
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 Complement System One of the body's lines of defense (immune system) involves white blood cells (leukocytes) that travel through the bloodstream and into tissues, searching for and attacking microorganisms and... read more , 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 Overview of Lymphoma Lymphomas are cancers of lymphocytes, which reside in the lymphatic system and in blood-forming organs. Lymphomas are cancers of a specific type of white blood cells known as lymphocytes. These... read more 
, or autoimmune disorders, such as systemic lupus erythematosus Systemic Lupus Erythematosus (SLE) Systemic lupus erythematosus is a chronic autoimmune inflammatory connective tissue disorder that can involve joints, kidneys, skin, mucous membranes, and blood vessel walls. Problems in the... read more 
(lupus) or dermatomyositis Autoimmune Myositis Autoimmune myositis causes inflammation and weakness in the muscles (polymyositis) or in the skin and muscles (dermatomyositis). Muscle damage may cause muscle pain and muscle weakness may cause... read more 
, 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.
Symptoms
The face, lips, tongue, the back of the hands or feet, genitals, and/or other areas of the body may swell. Typically, the swollen areas are slightly painful and not itchy. Hives do not appear. Swelling usually resolves in 1 to 3 days.
The membranes lining the mouth, throat, and airways may also swell. People may make a gasping sound when they breathe in. Such swelling can interfere with breathing and be life threatening. If these symptoms develop, people should see a doctor right away.
The membranes lining the digestive tract may also swell. Nausea, vomiting, and cramps are common.
This photo shows swelling of the lips in a person with hereditary angioedema.
By permission of the publisher. From Joe E, Soter N. In Current Dermatologic Diagnosis and Treatment, edited by I Freedberg, IM Freedberg, and MR Sanchez. Philadelphia, Current Medicine, 2001.
This person has a swollen tongue due to angioedema.
SCIENCE PHOTO LIBRARY
This person has swollen lips due to angioedema.
DR P. MARAZZI/SCIENCE PHOTO LIBRARY
Diagnosis
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.
Treatment
Drugs such as ecallantide, icatibant, or purified C1 inhibitor
Fresh frozen plasma
Drugs to prevent future attacks
Certain drugs, such as ecallantide, icatibant, 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 Plasma People are sometimes given transfusions of whole blood during severe bleeding (for example after an injury or pregnancy complications), but usually they are given only the blood component they... read more 
or, in the European Union, tranexamic acid 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.
C1 inhibitor, if available, may be given 1 hour before dental or surgical procedures instead of stanozolol or danazol.
The monoclonal antibody drug lanadelumab, given by injection, can be used to prevent attacks in people 12 years of age and older.
