Urticaria (Hives)

What is urticaria?

Urticaria is a condition in which red patches and wheals occur in the skin. The release of chemicals such as histamine from mast cells in the skin causes small blood vessels to leak fluid. This results in tissue swellings called wheals. The wheals can be a few millimetres or several centimetres in size, coloured white or red, often surrounded by a red flare, and frequently itchy.

Wheals may form rings, a map-like pattern or large patches. Each wheal may last a few minutes or several hours, and may change shape.

Does urticaria have any other names?

Yes. The common name is hives.

How common are hives?

Hives are very common affecting 2-3% of children. Most cases only last for a few days or weeks and get better without any treatment.

Are there different types of hives?

Hives are grouped into acute and chronic according to how long it has been present. Acute hives lasts for hours, days or a few weeks. Acute hives can occur as a dramatic rash which may worry both parents and doctors. The rash starts suddenly, frequently involves a large part of the skin and sometimes there is also swelling of hands, feet, and around the eyes. Chronic hives lasts for 6-8 weeks or more. In chronic hives the lesions are often not as dramatic as acute hives, but recur for days at a time, or in some cases are persistent or are present on most days.

What is the relation between hives and allergy?

Most cases of hives are NOT due to allergy and allergy tests are rarely helpful in finding a cause.

Acute hives is sometimes due to an allergy to medicines (most often antibiotics) or foods. Where there is not a clear history of reaction to a medicine or food the cause is often an infection which occurred 1-2 weeks earlier. This pattern is termed post infectious urticaria.

Chronic hives can be due to autoimmune disease (an immune reaction to oneself), and may be linked with other autoimmune conditions. In most autoimmune diseases antibodies against oneself (autoantibodies) usually develop. Antibodies are proteins that are produced by the immune system and circulate in the blood stream. In most cases of chronic hives tests for autoantibodies are negative and in this case the patient is said to have chronic idiopathic urticaria.

Are there any other types of hives?

Yes, physical urticaria refers to hives caused by external physical factors. The wheals usually take about 5-10 minutes to develop, and last 30 to 60 minutes. Triggers of physical urticaria can include pressure (stroking the skin), sweating, heat, cold and sunlight. Some people suffer from a mixture of different types of physical urticaria.

Do tests need to be done?

In many cases of acute hives, there may be no need for tests. Tests are usually not helpful in acute hives. Sometimes your doctor may order tests, particularly in cases of chronic hives.

The following tests are most commonly used:

• Blood count
• Thyroid autoantibodies (in chronic urticaria)
• Allergy tests
• Blood tests to see if there is bacterial infection

What is the treatment?

Treatment depends on the type of hives, how severe it is and how long it has been present.

The most common treatment is oral antihistamines. These medicines control whealing and itching for most patients with hives. They do not affect the underlying cause of the rash. Antihistamines may need to be taken intermittently or continuously until the underlying cause of the hives disappears. There are a number of different antihistamines and the response varies. If the first antihistamine is not effective, it might be necessary to increase the dose, or use a different antihistamine. Sometimes a combination of antihistamines works better than a single type alone. Chronic hives does not always respond well to antihistamine therapy.

Oral steroids (prednisone) in moderate dose for a few days may be helpful in severe cases of acute hives. They are rarely recommended long term because of potentially serious adverse effects. In rare cases, alternate day steroids may be needed.

In addition to drug treatment there are some general measures to follow. Do not take the medications your doctor has told you to avoid. In some cases aspirin, codeine and nonsteroidal anti-inflammatory drugs (for example ibuprofen) may make the hives worse. It is usually safe to take paracetamol.

Does dietary treatment have a role?

Dietary treatment is not necessary or helpful for acute hives.

A small proportion of cases of chronic hives are improved by the removal of colourings, preservatives and salicylates from the diet. If a diet is tried it is sometimes necessary to perform challenge tests to find out what foods need to be avoided in the long term. If the diet does not help it should not be continued.

What if my child developed hives when taking antibiotics?

Many cases of hives that occur at the same time as taking antibiotic ingestion are due to the infection rather than an allergy to the antibiotic. In the absence of formal antibiotic challenge it is often not possible to be certain about this. Antibiotic challenges for children with an urticarial rash following taking antibiotics should be supervised by an allergist.

Where can I find more information on the Internet?

• The Australian Society of Clinical Immunology and Allergy (ASCIA) website contains useful information on hives written by Australian specialists (www.allergy.org.au).
• DermNet NZ the web site of the New Zealand Dermatological Society has information about allergic skin diseases and hives (http://dermnetnz.org/)