Angioedema

Angioedema is swelling that is similar to hives, but the swelling is under the skin instead of on the surface.
Hives are often called welts. They are a surface swelling. It is possible to have angioedema without hives.
Causes.
Angioedema may be caused by an allergic reaction. During the reaction, histamine and other chemicals are released into the bloodstream. The body releases histamine when the immune system detects a foreign substance called an allergen.
In most cases, the cause of angioedema is never found.
The following may cause angioedema:
Hives and angioedema may also occur after infections or with other illnesses (including autoimmune disorders such as lupus, leukemia, and lymphoma).
A form of angioedema happens in families and has different triggers, complications, and treatments. This is called hereditary angioedema.