Hives fall into two categories: acute urticaria (ordinary hives which resolve after six to eight weeks) and chronic urticaria (which continue longer than six to eight weeks).
Ordinary urticaria (ordinary hives)
What are symptoms and signs 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."
What are the 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.) When a medication is implicated as a cause of hives, the drug must be stopped, since no skin or blood test will prove the connection. In most cases, drug-induced hives will go away in a few days. If a drug is stopped and the hives do not go away, this is a strong indication that the medication was not in fact the cause of the hives.
Some medications, like morphine, codeine, aspirin, and other nonsteroidal anti-inflammatory drugs (NSAIDs, such as ibuprofen [Advil]), 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 (defined as lasting six weeks or more) can last from months to years. The evaluation of this condition is difficult and allergy testing and other laboratory tests are rarely useful in such cases. The accurate evaluation of this condition requires the patient to give his or her physician precise information regarding their complete medical history, personal habits, and oral intake. Occasionally it may be necessary to limit specific foods or drugs for a time to observe any affect upon the skin condition. Certain systemic disease and infections may occasionally present in the skin as hives. If there is an inciting cause that can be determined, then specific treatments for that condition ought to be effective, or in the case of food or drug allergy, strict avoidance would be necessary. There are additionally rare forms of chronic urticaria that are produced when the patient makes antibodies against molecules on the surface of their own mast cells. There are tests available to identify this type of hives.
Physical urticaria is a type of chronic urticaria produced by physical stimuli. By far the most common form is dermographism, 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 dermographism, 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 exercise or physical exertion 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.
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Archived: March 20, 2014
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