Hives (Urticaria) & Angioedema Causes, Symptoms and Treatment on MedicineNet.com

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Hives
(Urticaria & Angioedema)

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Medical Author: Alan Rockoff, MD
Medical Editor: Melissa Conrad Stöppler, MD

Are Hives Always Caused by an Allergy?

Medical Author: Melissa Conrad Stöppler, MD
Medical Editor: William C. Shiel Jr., MD, FACP, FACR

Read about the causes, symptoms, and treatment of hives. Hives are swollen, red or pink bumps, patches, or welts on the skin that usually appear suddenly. Itching is the most common symptom associated with hives, although some people report that hives cause a stinging or burning sensation. Hives are a very common reaction to all kinds of stimuli. While an allergic reaction can be a cause of hives, in the majority of outbreaks, the exact cause of hives is not known. Hives are also known as urticaria.

Hives form when a chemical called histamine is released by specialized cells known as mast cells. It is true that allergic reactions ultimately lead to the release of histamine, but other circumstances can result in the release of histamine, causing an outbreak of hives. Histamine acts by causing blood vessels to leak fluid into the nearby tissues. In the skin, small areas of swelling develop as a result of capillary (the smallest blood vessels) leakage.

In addition to allergic reactions to medications, foods, or other substances, hives may be triggered by direct physical stimulation such as temperature extremes, water, sun, and physical exercise. Having a viral infection can also cause an outbreak of hives, and even stress and nervousness have been associated with hives outbreaks. In the form of hives known as dermographia, or "skin writing," raised, itchy red welts with adjacent flares appear wherever the skin is scratched or where belts and other articles of clothing rub against the skin.

Find out how hives are treated »

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What are hives (urticaria)?

Hives (medically known as urticaria) are red, itchy, raised areas of skin that appear in varying shapes and sizes. They range in size from a few millimeters to several inches in diameter. Hives can be round, or they can form rings or large patches. Wheals (welts), red lesions with a red "flare" at the borders, are another manifestation of hives. Hives can occur anywhere on the body, such as the trunk, arms, and legs.

It is estimated that 15% of all people will develop urticaria at some point in their lives. Of those with chronic hives, some 80% are idiopathic, the medical term which means that no cause, allergic or otherwise, can be found.

One hallmark of hives is their tendency to change size rapidly and to move around, disappearing in one place and reappearing in other places, often in a matter of hours. Individual hives usually last two to 24 hours. An outbreak that looks impressive, even alarming, first thing in the morning can be completely gone by noon, only to be back in full force later in the day. Very few, if any other skin diseases occur and then resolve so rapidly. Therefore, even if you have no evidence of hives to show the doctor when you get to the office for examination, he or she can often establish the diagnosis based upon the history of your symptoms. Sometimes it is helpful to bring along a photograph of what your rash looked like at its worst.

Swelling deeper in the skin that may accompany hives is called angioedema. This may be seen on the hands and feet as well as on mucous membranes (with swelling of the lips or eyes that can be as dramatic as it is brief.)

What causes hives?

Hives are produced by histamine and other compounds released from cells called mast cells, which are a normal part of skin. Histamine causes fluid to leak from the local blood vessels, leading to swelling in the skin.

Hives are very common. Although they can be annoying, they usually resolve on their own over a period of weeks, and are rarely medically serious. Some hives are caused by allergies to such things as foods, medications, and insect stings, but the large majority of cases are not allergic, and no specific cause for them is ever found. Although patients may find it frustrating not to know what has caused their hives, maneuvers like changing diet, soap, detergent, and makeup are usually not helpful in preventing hives and for the most part are not necessary.

In rare cases (some hereditary, others caused by bee stings or drug allergy), urticaria and angioedema are accompanied by shock and difficulty breathing. This is called anaphylaxis. Ordinary hives may be widespread and disturbing to look at, but the vast majority of cases do not lead to life-threatening complications.