Why do angioedema and hives usually happen together?

Skin allergy: Both hives and angioedema can be caused by the same mechanism: the release of histamine and other allergic chemicals from mast cells that bind allergic antibody (ige). There are also other non-allergic causes for both hives and angioedema.

Hives/Angioedema: Both are typically triggered by the same mechanism which is the release of histamine from mast cells and basophils.