Angioedema is similar to hives but affects deeper skin layer. Hives (also called urticaria) are red, itchy, and raised areas of the skin of varying shapes and sizes. Hives are the result of histamine and other compounds that are released from cells called mast cells. Histamine causes serum to leak from the local blood vessels, which causes swelling in the skin. Hereditary angioedema is a genetic form of angioedema. Persons with hereditary angioedema are born lacking an inhibitor protein (called C1 esterase inhibitor) that normally prevents activation of a cascade of proteins leading to the swelling of angioedema. They can develop recurrent attacks of swollen tissues, pain in the abdomen, and swelling of the voice box (larynx) which can compromise breathing.