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Angioedema is a disorder that affects the deeper layers of the skin and triggers significant swelling, particularly in the hands, face and feet. Sometimes, angioedema appears in tandem with hives (urticaria). Hives are raised, red, itchy welts that form on the skin in response to an allergic reaction.

There are three types of angioedema:

• Allergic angioedema. Often simply called angioedema, this involves deep tissue swelling caused by an allergic reaction. Mast cells (cells involved in allergic reactions) release histamine and other chemicals into the bloodstream, which causes capillaries (tiny blood vessels) to dilate and leak fluids through their walls and into the dermis and subcutaneous tissues of the skin. This causes tissue swelling that usually appears in the soft tissues of the lips and other parts of the mouth, throat, eyelids, genitals, hands and feet. Hives and itching often accompany allergic angioedema.
  
  

  

• Hereditary angioedema. A genetic disorder associated with a deficiency of the blood protein C1 inhibitor. This protein belongs to a group collectively known as the complement system, which is involved in immune system function. A deficiency of C1 inhibitor hampers the normal flow of blood and lymphatic fluid, triggering swelling in local areas of skin and the tissue beneath it. Mucous membranes that line the body openings (such as the mouth) also are vulnerable. Hereditary angioedema often first develops during puberty.
  
  Sometimes, swelling of the upper airways occurs, which causes breathing problems that can become life-threatening. Hives and itching are not usually associated with hereditary angioedema. Androgens (male sex hormones such as testosterone) are among the medications used to prevent attacks. Treatments associated with allergic angioedema usually have little value in treating hereditary angioedema.
  
  
• Idiopathic angioedema. Swelling caused by unknown factors or by exposure to certain medications. Certain medications used to treat high blood pressure, called angiotensin-converting enzyme (ACE) inhibitors, increase the blood chemical bradykinin, which widens blood vessels. Increased bradykinin levels can cause angioedema in some patients. Hives typically accompany this form of angioedema.

An episode of angioedema typically lasts from a few hours to a few days. In some people, however, angioedema can be chronic (ongoing), recurring over weeks or months.

Angioedema symptoms are usually relatively mild and resolve by themselves. However, in rare cases, swelling in the mouth and throat can cause breathing problems and blood pressure can drop as a result of fluid moving out of the blood. This is potentially life-threatening and requires emergency medical treatment.