Urticaria

Causes of urticaria

There are distinct types of urticaria:

• Acute urticaria may be caused by an allergy and can last between several hours and six weeks
• Chronic urticaria isn't usually caused by an allergy and persists beyond six weeks
• Physical urticaria is triggered by physical factors and lasts only an hour or two

The most likely triggers for acute urticaria are allergies to pets, horses, latex and foods, such as shellfish and nuts in adults and eggs and cow's milk in children. 

Other possible causes include bee or wasp stings, and allergies to medicines such as antibiotics, blood pressure pills and aspirin. 

Viral infections, such as glandular fever and herpes, dental and sinus infections, fungal infections, blood transfusions and vaccines can also cause acute urticaria. 

The cause of chronic urticaria is often more difficult to identify. Most cases are called chronic idiopathic urticaria, which means they're caused by the body's unexplainable development of antibodies to itself (auto-antibodies).

Chronic bacterial and parasitic infections, long-term use of blood pressure drugs, underlying thyroid disease and autoimmune diseases such as lupus can provoke urticaria. 

Chronic urticaria is often accompanied by coexistent physical urticaria, triggered by environmental exposure to heat, cold, sunlight, vibration, pressure on the skin or even exercise.

Most people with urticaria have such sensitive skin that any rubbing will cause raised red lines to develop. This is called dermatographism.

Urticaria symptoms

The rash is very itchy and consists of a number of raised pale bumpy weals surrounded by red skin. Ordinary urticaria tends to move about or migrate all over the skin surface. In chronic cases, the itchiness may cause sleepless nights and lead to depression. 

The condition tends to settle and then relapse again at times of viral illness, stress and after taking medication that contains aspirin. This chronic pattern may recur for many years.

Tissue swelling, called angioedema, may occur with urticaria. This affects the lax tissues around the eyelids, lips, neck and groin. Occasionally, an inherited deficiency of the C1 esterase inhibitor enzyme leads to marked swelling without urticaria. This rare condition is called hereditary angioedema.

If urticaria doesn't disappear after a few weeks, or doesn't respond to antihistamine medication, and is accompanied by any other health problem, see your GP. Blood tests may be able to identify an allergy or underlying immune disease.

Urticaria treatments

High doses of non-sedating antihistamines may be necessary for prolonged periods of up to six weeks or more. Short courses of oral steroids are occasionally required to settle severe symptoms. 

Try to avoid general urticaria triggers such as stress, alcohol, aspirin, hot baths, rapid temperature changes, tight clothing and junk or processed foods containing sulphur dioxide, sodium benzoate, salicylate and tartrazine. 

Avoid tomatoes, strawberries, strong cheese, dark fish and fermented foods. Although these 'pseudo-allergens' aren't the primary cause of urticaria, they do tend to aggravate it.

The new leukotriene receptor antagonist medications used in asthma may also help urticaria if used in conjunction with antihistamines.

If there's no response to conventional treatment, a specialist should investigate other possible underlying illnesses, such as lupus, thyroid disease and chronic infections.