Hives (urticaria) is a common skin rash characterised by one or many weals of reddened, raised and itching skin. The weals can vary in size, from relatively small to as large as a dinner plate. The weals 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 weals generally appear in clusters, with one cluster getting worse as another gets better.
Most weals disappear without a trace within a few hours, only to be replaced by a new one elsewhere on the skin. Weals 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 weals may come and go for a few days or weeks. Rarely, they persist for more than six weeks. Chronic hives is much less common. The weals come and go for months or even years.
It is thought that around one in every six people will experience an attack of acute hives at some point in their lives. In most people this is not due to allergy.
Acute hives can be triggered by a number of different factors. Common causes include respiratory infections (particularly in young children), contact with animals or plants, allergic reactions to foods or medication (particularly pain relievers and antibiotics), and sometimes, insect stings, heat or cold, stress, food additives or preservatives.
In chronic hives, it is rare to find a cause, although aspirin and codeine may aggravate it.
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 are like land-mines, and contain bags filled with 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 weals that look like mosquito bites – these are red on the outer rim and white in the centre, and each weal lasts for around two to four hours (rarely up to 24 hours). Weals appear in batches or clusters, and as one batch fades away as 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 per cent of cases the cause of hives is unknown. Some factors known to cause hives include:
- medication – such as antibiotics, aspirin and codeine
- some food additives
- infections – including bacterial, viral or parasitic
- certain underlying conditions – such as systemic lupus erythematosus, rubella and hepatitis
- emotional stress
- contact with plants or animals
- cold temperatures
- exercise and sweating
- bee and wasp stings.
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 two, three or even four 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 doctor
- Clinical immunology/allergy specialist
This page has been produced in consultation with and approved by:
Australasian Society of Clinical Immunology and Allergy (ASCIA)
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