Hives

About hives

Hives (urticaria) are common skin rashes characterised by one or many wheals (lumps) of reddened, raised and itching skin. The wheals can vary in size, from relatively small to as large as a dinner plate. The wheals may be circular, oval or annular (ring-shaped).

Hives can affect any part of the body, but is common on the torso, throat, arms and legs. The wheals generally appear in clusters, with one cluster getting worse as another gets better.

Most wheals disappear without a trace within a few hours, only to be replaced by a new one elsewhere on the skin. Wheals that persist in exactly the same spot for more than 24 hours may indicate a different disorder known as urticarial vasculitis.

In acute (short-lived) hives, the wheals may come and go for a few days or weeks. In rare cases of chronic hives, wheals may persist for more than 6 weeks. The wheals come and go for months or even years.

It is thought that around one in every 6 people will experience an attack of acute hives at some point in their lives. In most people this is not due to allergy.

Mast cells and histamines

Underneath the lining of the skin, gut, lungs, nose and eyes are mast cells. These are designed to kill worms and parasites.

Mast cells contain chemicals including histamine. When these are released into the skin in small amounts, they cause itching and irritation. When large amounts are released into the skin, fluid leaks out of blood vessels, resulting in swelling of the skin (hives).

Occasionally, hives produce swelling without an itch.

Symptoms of hives

Symptoms of hives include:

• raised circular wheals that look like mosquito bites – these are red on the outer rim and white in the centre, and each wheal lasts for around 2 to 4 hours (rarely up to 24 hours). Wheals appear in batches or clusters, and as one batch fades away a new batch appears
• localised itching
• with acute urticaria, the rash may last for days or weeks
• with chronic hives, the rash may persist for months to years, occasionally decades.

Causes of hives

In 80% of cases the cause of hives is unknown. Some factors known to cause hives include:

• medication – such as antibiotics, aspirin and codeine
• allergic reactions to foods
• some food additives
• infections – including bacterial, viral or parasitic
• respiratory infections (particularly in young children)
• certain underlying conditions – such as systemic lupus erythematosus, rubella and hepatitis
• emotional stress
• contact with plants or animals
• heat
• cold temperatures
• exercise and sweating
• bee and wasp stings.

In chronic hives, it is rare to find a cause, although aspirin and codeine may aggravate it.

Treatment for hives

If a trigger is identified and it is possible to avoid that trigger, then the hives will resolve. Where no trigger is found, or the trigger cannot be avoided, treatment may include:

• avoidance of factors that make the condition worse – such as aspirin, codeine, sunshine, heat and hot showers
• antihistamines – some people require 2, 3 or even 4 tablets a day to control hives. These are available from pharmacies without prescription. Some antihistamines cause drowsiness.

For chronic hives, there are a number of other medications that can be prescribed.

Where to get help

• Your GP (doctor)
• Dermatologist
• Australasian Society of Clinical Immunology and Allergy (ASCIA) – Locate a specialist