Angioedema is a deep, short-lived swelling that can occur anywhere below or within the skin. Skin angioedema swellings are usually pale and uncomfortable rather than red and itchy. They generally last longer than superficial weals and often for days. Angioedema can also occur below mucous membranes of the mouth and genitalia. In rare situations, it can affect the bowel and bladder causing pain due to obstruction without being visible. Angioedema may be a feature of urticaria where it is due to histamine release from mast cells and responds to the same treatments as weals. It may also be a feature of anaphylaxis if it causes choking as a result of swelling within the throat. However, if angioedema occurs without weals it may be caused by a completely different mediator called bradykinin.

This may cause abdominal pain or throat swellings, which need completely different treatments from urticaria. Doctors try to understand from the story whether angioedema occurs with or without weals since this helps them to work out whether the swellings are due to histamine or bradykinin but it can be difficult to tell. A proportion of patients with bradykinin-induced angioedema will have inherited their condition. This is known as hereditary angioedema. Three types are currently recognized with different laboratory findings (Type I, II and III). About 50% of the children of affected patients are at risk of carrying the genetic abnormality that results in a reduction in function of an important enzyme inhibitor that controls several pathways necessary for good health.