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Hereditary angioedema has no known cause other than a family history of this genetic condition.

Allergic angioedema occurs when an allergic reaction is triggered by one of many common allergens (harmless substances that trigger an exaggerated immune system reaction). It is not always easy to trace the source of an outbreak. Still, patients should try to be aware of the circumstances surrounding a bout of angioedema to determine which allergens might be responsible. Common angioedema triggers include the following:

• Allergy shots (immunotherapy). Allergy shots are a form of allergy treatment in which low doses of an allergen are injected into a patient over a period of time in an attempt to build up a tolerance to the allergen. Occasionally, allergy shots can actually trigger angioedema.
  
  
• Certain foods. Common food allergies can cause allergic angioedema, including allergies to cow’s milk, eggs, peanuts, wheat, soybeans, fish, shellfish, berries and tree nuts. Foods containing sulfides (e.g., maraschino cherries, frozen or dried potatoes) can also trigger the condition.  
  
  
• Environmental factors. Cold, heat, sunlight or water can cause angioedema in some people.
  
  
• Infections, injury and illness. These may include autoimmune disorders (such as lupus or cancer), leukemia, thyroid disorders, colds, and infections such as hepatitis B or C.
  
  
• Insect stings or bites. Allergies to venom released in the stings and bites of bees, yellow jackets, hornets, wasps and fire ants can trigger allergic angioedema.
  
  
• Latex. Natural rubber used in many products. Latex allergies may cause angioedema.
  
  
• Physical factors. Pressure on the skin or scratches to the skin can result in raised lines that result from histamine-based angioedema that causes swelling beneath the skin. This condition is known as dermatographism, which means “write on the skin.” Physical strain (e.g., intense exercise, prolonged writing, mowing the lawn) can also trigger the condition. In women, angioedema may be caused by pregnancy and menstruation.
  
  
• Pollen. A common cause of allergic rhinitis (hay fever), allergies to pollens can also cause allergic angioedema.
  
  
• Some medications. Many medications can trigger angioedema, including penicillin and other antibiotics, painkillers (particularly aspirin and ibuprofen), angiotensin-converting enzyme (ACE) inhibitors and others. Over-the-counter medications, such as aspirin, nonsteroidal anti-inflammatory drugs (NSAIDs) and cold medicine with acetylsalicylic acid, can also cause the condition. Symptoms may not occur for days to months after a patient first starts taking the drug.
  
  
• Stress. Emotional stress can trigger symptoms related to angioedema.
  
  
• Surgery and other medical procedures.   

Risk factors for developing angioedema include a family history of this condition or other allergies. In addition, a person who has had angioedema or other allergic reactions in the past has a higher likelihood of developing angioedema in the future.

In a significant percentage of cases, the trigger for allergic angioedema remains a mystery. In some cases, angioedema is an indicator of an underlying condition such as leukemia or a connective tissue disorder.