Swelling to the subdermal/subcutaneous layers of the skin
Inflammation is typically mediated by bradykinin and histamine
Inflammatory mediators promote vasodilation, vascular leakage and tissue swelling
Mechanisms of activation vary. Can be allergic (IgE related) or due to deficiencies in mechanisms that switch off inflammatory cascade e.g C1 esterase inhibitor deficiency and potentiation of bradykinin with ACE inhibitors