Hives, also known as urticaria, are raised welts that can occur anywhere on the body. They range in size from small to large, 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.
Both hives and angioedema can be caused by the immune system overreacting to a normally harmless substance. During this reaction, a chemical called histamine is released 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, blood vessel walls change during that process, allowing plasma — the liquid portion of blood — to flow into the skin. This influx of fluid is what causes swelling in both hives and angioedema.
For the most part, these swellings are harmless. There are severe cases, however, when emergency medical care is needed, such as when hives are painful and have been present for more than a week, are accompanied by other symptoms like abdominal pain, or if swelling affects the throat and mouth, restricting the airway and making breathing difficult.
Immediate first aid and medical attention are needed if anaphylactic shock occurs, or if the swelling blocks the airway and fully prevents breathing.
Hives vs. angioedema
The main difference between hives and angioedema is that in hives swelling affects the more superficial layers of the skin, whereas in angioedema deeper skin layers are the ones that are affected. Both conditions may occur simultaneously.
Unlike hives, swelling tied to angioedema usually is not intensely itchy or painful on its own, but the welts tend to last longer (up to three days), while hives subside after a day in most cases.
Hives are caused most often by an allergic reaction, while angioedema can have a range of causes, including being triggered by certain medications, being associated with some immune disorders, and even occur as a result of genetic mutations, or being triggered by an allergic reaction.
Diagnosing hives and angioedema
Hives and angioedema usually are diagnosed following a general examination of the skin. Also, allergy tests may be used to identify what is triggering the reaction. These include skin prick tests, in which different allergens — substances seen as a potential threat by the immune system — are placed over a person’s skin. If the skin becomes itchy, turns red, or swells, it means the person is likely allergic to that substance.
Blood tests looking for specific antibodies in the bloodstream also may be used. Antibodies are naturally produced by the immune system to fight off allergens. However, when the body makes too many, it can cause hives and angioedema.
Treating hives and angioedema
Both hives and some types of angioedema can be treated with normal allergy medications such as antihistamines, corticosteroids, and epinephrine (EpiPen). EpiPens can be used to rapidly treat individuals experiencing a life-threatening swelling.
If swelling is caused by hereditary angioedema — a form of angioedema that does not have an allergic 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 swelling is 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 potential triggers. These include certain foods or liquids, airborne allergens, detergents and soaps with scents or dyes, extreme temperature changes, stress, and wearing tight and heavy clothes.
Last updated: Dec. 7, 2021
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