Hives, also known as urticaria, affects about 20 percent of people at some time during their lifetime. Hives can start as itching, followed by swollen, red welts. The itching may be mild to severe. Scratching, alcoholic beverages, exercise, and emotional stress may worsen the itching.
Hives symptoms can come and go, lasting minutes, hours, days, several weeks, months or even years. There are two types of hives, depending on how long they last:
- Acute urticaria: hives that last six weeks or less
- Chronic urticaria: hives that last or recur for more than six weeks
In general, the causes of acute and chronic hives are very different.
What causes hives, and how long do hives last?
Acute hives last six weeks or less and are generally caused by the following:
In most of these cases, the hives resolve when the cause is avoided, removed or treated.
Chronic hives last more than six weeks. In many cases, the cause of chronic hives cannot be identified despite detailed history and testing. This condition is called idiopathic urticaria. The immune system is the cause of about 50 percent of hives that are not identified. In other cases, chronic hives may be associated with thyroid disease, other hormonal problems, or rarely cancer. In most cases, chronic hives will gradually disappear over time.
A type of chronic hives is “physical urticaria” in which hives can have one or more physical cause. These may include:
- Rubbing or scratching (dermographism). This is the most common reason for chronic hives. These physical hives appear within a few minutes along the path of rubbing or scratching and last less than an hour.
- Constant pressure (pressure urticaria). Hives can also appear as red swelling caused by belts and constrictive clothing such as sock bands. In some occupations they occur in parts of the body under constant pressure, such as the knees in tile-layers or the hands in carpenters.
- Change in temperature. Hives may be caused by heat or cold. Hives called cold urticaria are caused by exposure to low temperature followed by re-warming. This can be severe and life threatening if there is a general body cooling, for example after a plunge into a swimming pool. Hives called cholinergic urticaria are due to an increase in body temperature with sweating, exercise, hot showers, and/or anxiety.
- Sun exposure (Solar urticaria). Hives may occur within a few minutes after exposure to the sun.
Inflammation of the blood vessels, called vasculitis, can also cause hives. These hives are more painful than itchy. These painful hives may leave a bruise on the skin and often last more than 24 hours.
How are the causes of hives identified?
In some cases the cause is obvious – a person eats peanuts or shrimp, and then develops hives within a short time. Because there are so many possible causes for hives, other cases require detective work by the patient and physician. In some cases, the cause cannot be identified.
When hives involve swelling of the tongue or trouble breathing, immediate evaluation in the emergency room is required.
A single episode of hives does not usually need extensive testing. If hives reoccurs, your doctor will evaluate possible causes. If food allergy is suspected, a diary of foods eaten within a few hours before the hives started may be extremely helpful.
Chronic hives should be evaluated by an allergist. The allergy specialist will take your detailed medical history and your family’s medical history. This will include exposures from your work and home environment, and current and recent medications. The allergist will examine you for possible causes of hives. In some cases you may need skin tests, blood tests and urine tests. Allergy skin testing may provide useful information in some cases. Rarely, if food allergies are suspected, an elimination diet, and/or oral food challenge may be required. In cases where vasculitis is suspected a skin biopsy may be helpful.
The specific cause of chronic hives can be identified in about 20 percent of cases. Ongoing research will allow us to identify more causes and more effective treatments for hives.
What is the treatment for hives?
In most instances, hives will improve with medications such as antihistamines. Low-sedating or non-sedating antihistamines are preferred. They are effective, long-lasting (may be taken once a day), with fewer side effects. Frequently, your physician may try a combination of two or three antihistamines for the treatment for hives. Severe episodes of urticaria may require temporary treatment with prednisone, a similar corticosteroid medication or immune modulator.
If your hives rash involves swelling of the tongue or lips, or you have trouble breathing, an epinephrine self-injector will be prescribed for you to carry.
If the cause of hives can be identified, the best treatment is to avoid or eliminate it. Below are examples:
- Foods: If a problem with a specific food is strongly suspected, then you should not eat that food. This will require you to carefully read packaged food labels and question restaurant staff about ingredients in meals.
- Rubbing or scratching: Avoid harsh soaps and tight clothing. Frequent bathing may reduce the problem of dry skin, which can cause itching and scratching that can aggravate this condition.
- Constant pressure: Loose-fitting clothing will help relieve hives caused by pressure urticaria.
- Change in temperature: If your hives are caused by cold, you should not swim alone. If you have severe cold urticaria, you should not swim at all. Cold air exposure should be avoided if possible, and warm clothing should be worn.
- Sun exposure: Wear protective clothing and apply sun block when outdoors.
- Medications: If you have a problem with a specific medication, stop taking it and notify your doctor and your pharmacist.
In most chronic urticaria, there is no external cause identified. Daily use of antihistamines is preferred to taking them only after a break out.
If you need more information about how to treat hives, or have any questions, your allergist will be happy to answer them.
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