Hereditary angioedema is an asymmetrically localized disease that can progress with swelling (edema) of the skin and internal organs without urticaria (hives). Instead of itching, pain and a feeling of tension are at the forefront. Hereditary angioedema occurs by mechanisms different from the development of allergic diseases. Hereditary angioedema occurs when the amount of “C1 inhibitor” in the blood is low or its function is impaired. In the absence or poor functioning of C1 inhibitor, there is an increase in bradykinin, which is a very effective vasodilator. Hereditary angioedema is inherited. While the majority of patients had low C1 inhibitor levels (type I), while in a minority the C1 inhibitor is functionally deficient (type II). In recent years, a new type associated with Factor XII mutation (III) has been described, but its mechanism has not been fully elucidated.

Angioedema may be acquired, especially in patients with lymphoproliferative and malignant diseases in late life or in those who develop auto-antibodies against C1 inhibitor. Angioedema may also develop in association with angiotensin converting enzyme inhibitors (ACE-I) used as antihypertensive drugs. In some patients who develop angioedema, the cause may not be fully demonstrated.