What Causes Urticaria and Angioedema?

Just about every patient I see has some suspicion of what could be causing their hives. Most are concerned with some type of food allergy, some think that a medication or environmental trigger (such as an odor or chemical) is the cause, while others are concerned with a physical trigger, such as heat or cold. While any of the above triggers are possible, the most common cause of acute hives (those lasting less than 6 weeks) are viral infections (such as the common cold), and the most common cause of chronic hives (those lasting greater than 6 weeks) are autoimmune causes.