Hives or urticaria are raised welts that can occur in a range of sizes, from small to large to a mass known as a plaque. They usually are a different color and texture from the surrounding skin, and are itchy and uncomfortable. Usually the result of an allergic reaction, they sometimes can be seen with — and mistaken for — another type of skin swelling known as angioedema.

What causes skin swellings?

Both hives and angioedema can be caused by the immune system reacting to an injury, illness, or irritation, or overreacting to a normally harmless substance. During this reaction, it releases a chemical called histamine into the skin.

Histamine activates a chain of events that lead to blood vessels in the skin dilating (widening) and letting more blood into the tissues. This causes the flushed color and warm sensation that sometimes accompanies  hives.

In addition, the walls of the blood vessels are changed so that plasma, the clear part of the blood, can flow into the skin. This influx of fluid is what causes the swelling in both hives and angioedema.

For the most part, these swellings are harmless. There are, however, severe cases where emergency medical care is needed, such as:

  • if hives are painful and have been present for longer than 25 hours.
  • if there are changes to the skin after swelling has gone away.
  • if abdominal pain is present.
  • if swelling in the throat and mouth causes breathing difficulties.

If anaphylaxis or shock occurs, or if the swelling blocks the airway and prevents breathing completely, then immediate first aid and medical attention are needed.

What is the difference between hives and angioedema?

The main difference between hives and angioedema is that hives swell at a shallower layer of the skin than angioedema. The two can occur simultaneously, and hives sometimes will occur on top of the angioedema-affected skin.

Unlike hives, angioedema swellings usually are not intensely itchy or painful on their own ,but they tend to last for a longer period of time (up to three days), while hives subside after a day in most cases.

Hives are caused most often by an allergic reaction (particularly to medications) while angioedema swellings can have a range of causes, including a reaction to certain medications, immune disorders, and even genetic mutations, in addition to being triggered by allergens.

How are hives or angioedema treated?

Both hives and some types of angioedema swellings can be treated or brought down with normal allergy medications such as antihistamines, corticosteroids, and epinephrine (EpiPen). EpiPens can be used to immediately treat individuals with a life-threatening swelling.

In case angioedema swellings are not allergic in origin, they will not respond to these medications. If this kind of angioedema occurs, Firazyr (icatibant) can be used in much the same way as an EpiPen.

If the swellings are not life-threatening, both hives and angioedema typically will fade on their own and any itching and discomfort can be managed with skin creams as needed.

Treatment and management of both types of swellings include avoiding allergens or other triggers that might have caused the swelling. A skin test can help determine what an individual is allergic to and what to avoid.

