avoidance of factors that make the condition worse – such as aspirin, codeine, sunshine, heat and hot showers. Where no trigger is found, or the trigger cannot be avoided, treatment may include: If a trigger is identified and it is possible to avoid that trigger, then the hives will resolve. In chronic hives, it is rare to find a cause, although aspirin and codeine may aggravate it. certain underlying conditions – such as systemic lupus erythematosus, rubella and hepatitis. respiratory infections (particularly in young children). infections – including bacterial, viral or parasitic. medication – such as antibiotics, aspirin and codeine. Some factors known to cause hives include: In 80% of cases the cause of hives is unknown. with chronic hives, the rash may persist for months to years, occasionally decades. with acute urticaria, the rash may last for days or weeks. Wheals appear in batches or clusters, and as one batch fades away a new batch appears 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). Occasionally, hives produce swelling without an itch. When large amounts are released into the skin, fluid leaks out of blood vessels, resulting in swelling of the skin (hives). When these are released into the skin in small amounts, they cause itching and irritation. Mast cells contain chemicals including histamine. These are designed to kill worms and parasites. 
Underneath the lining of the skin, gut, lungs, nose and eyes are mast cells.
In most people this is not due to allergy. It is thought that around one in every 6 people will experience an attack of acute hives at some point in their lives. The wheals come and go for months or even years. In rare cases of chronic hives, wheals may persist for more than 6 weeks. In acute (short-lived) hives, the wheals may come and go for a few days or weeks. Wheals that persist in exactly the same spot for more than 24 hours may indicate a different disorder known as urticarial vasculitis. Most wheals disappear without a trace within a few hours, only to be replaced by a new one elsewhere on the skin. The wheals generally appear in clusters, with one cluster getting worse as another gets better. Hives can affect any part of the body, but is common on the torso, throat, arms and legs. The wheals may be circular, oval or annular (ring-shaped). The wheals can vary in size, from relatively small to as large as a dinner plate. Hives (urticaria) External Link are common skin rashes characterised by one or many wheals (lumps) of reddened, raised and itching skin.
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