Angioedema is a swelling in the deep layers of the skin or mucous membranes, which occurs most commonly in the area around the eyes, lips, tongue, hands, feet or genitals. In more severe cases, the swelling may affect the upper respiratory tract or intestines. 

The condition is caused by small blood vessels becoming more permeable, or leaky. The fluid that leaks from the vessels builds up in the tissues, causing a swelling known as edema. This can be triggered by a variety of factors, such as food and medications. Angioedema may also be the result of a hereditary condition.

There are several different types of angioedema for which the underlying cause may differ, but the result is the same. The types of angioedema are acute allergic angioedema, non-allergic drug reaction, hereditary angioedema, acquired C1 inhibitor deficiency.

For another type of angioedema, called idiopathic angioedema, the cause is not known. Research suggests that as many as half of idiopathic angioedema cases may be associated with autoimmune disorders such as systemic lupus erythematosus.

Acute allergic angioedema

Allergic angioedema can be triggered by foods, especially nuts, shellfish, milk or eggs; medications including penicillin, sulfa drugs, or aspirin; insect venom from a bite or sting; or natural rubber latex products such as gloves.

In the allergic reaction, a type of cell known as mast cells are activated. These cells release chemicals including histamine that increases the leakiness of small blood vessels and causes edema.

Non-allergic drug reaction

A type of medication used to treat high blood pressure, called angiotensin-converting enzyme (ACE) inhibitors, may cause angioedema. The medication blocks the breakdown of a chemical in the body called bradykinin, which causes blood vessels to widen, or dilate. Bradykinin also increases the permeability of small blood vessels, leading to edema.

Only a small number of people who take ACE inhibitors develop angioedema; this may be due to differences in how their bodies metabolize bradykinin.

Hereditary angioedema

Someone with hereditary angioedema has inherited a gene that reduces the levels or function of a protein in the blood called C1 inhibitor.

The C1 inhibitor protein prevents a chain of chemical reactions in the blood known as the kallikrein-kinin system. This system plays a role in inflammation, blood pressure control, and blood clotting. The system’s activation leads to the formation of bradykinin, which increases blood vessel leakiness and causes edema.

There are two types of hereditary angioedema. Both involve mutations in the SERPING1 gene, which contains the information for producing the C1 inhibitor protein.

In type 1 hereditary angioedema, mutations in the SERPING1 gene lead to reduced blood levels of C1 inhibitor. In type 2 hereditary angioedema, the C1 inhibitor is produced but due to a mutation in a particular region of the gene, the protein does not function as it should.

Acquired C1 inhibitor deficiency

Sometimes, people without a defect in the SERPING1 gene still develop, or acquire, low levels of C1 inhibitor. This is due to an increased breakdown of the protein, and resulting low blood levels lead to angioedema.

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