Hives (cont.)

What are the different kinds of hives?

Almost all hives fall into two categories: ordinary urticaria (ordinary hives) and physical urticaria (physical hives).

Ordinary urticaria (ordinary hives)

Symptoms of ordinary hives

Ordinary hives flare up suddenly and usually for no specific reason. Welts appear, often in several places. They flare, itch, swell, and go away in a matter of minutes to hours, only to appear elsewhere. This sequence may go on from days to weeks. Most episodes of hives last less than six weeks. Although that cutoff point is arbitrary, hives that last more than six weeks are often called "chronic."

Causes of ordinary hives

As noted above, many cases of ordinary hives are "idiopathic," meaning no cause is known. Others may be triggered by viral infections. A few may be caused by medications, usually when they have been taken for the first time a few weeks before. (It is uncommon for drugs taken continuously for long periods to cause hives or other reactions.)

Some medications, like morphine, codeine, aspirin, and other nonsteroidal anti-inflammatory drugs (NSAIDs, such as ibuprofen), cause the body to release histamine and produce urticaria through nonallergic mechanisms.

Despite the reputation hives have for being "allergic," when there is no obvious connection between something new that a person has been exposed to and the onset of hives, allergy testing is not usually helpful.

Chronic hives

Chronic hives can last from months to years. Allergy testing and laboratory tests are hardly ever useful in such cases.

Physical urticaria (physical hives)

The term physical urticaria refers to hives produced by direct physical stimulation of the skin. By far the most common form is "dermographia," which literally means "skin writing." This is an exaggerated form of what happens to anyone when their skin is scratched or rubbed: a red welt appears at the line of the scratch. In dermographia, 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, causing mast cells to leak histamine.

Another common form of physically induced hives is called cholinergic urticaria. This produces hundreds of small itchy bumps. These occur within 15 minutes of physical exertion, or a hot bath or shower, and are usually gone before a doctor can examine them. This form of hives happens more often in young people.

Other forms of physical hives are much less common. Triggers for these include cold, water, and sunlight.

Next: What is the treatment for hives? »

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