Angioedema occurs when the immune system overreacts to a harmless substance, called an allergen. The immune system is made up of special cells, called white blood cells, which fight infection. When an allergen is present in the body, white blood cells recognize the allergen, and release chemicals into the blood stream. These chemicals can cause inflammation of the skin, nose, throat, lungs or intestines.

Underlying causes include:

• Allergic reactions to insect stings
• Allergic reactions to drugs (particularly ACE inhibitors and antibiotics)
• Allergic reactions to foods