What causes acute urticaria?
A ‘trigger’ causes cells in the skin to release chemicals such as histamine. The chemicals cause fluid to leak from tiny blood vessels under the skin surface. The fluid pools to form weals. The chemicals also cause the blood vessels to open wide (dilate) which causes the flare around the weals. The trigger is not identified in about half of cases. Some known triggers include: • Allergies – for example: • Food allergies such as allergies to nuts, strawberries, citrus fruit, egg, food additives, spices, chocolate, or shellfish. Sometimes you can develop an allergy to a food even if you have eaten it without any problem many times before. • Allergies to insect bites and stings. • Allergies to medicines such as penicillin, aspirin, anti-inflammatory painkillers, etc. • A viral infection such as a cold or ‘flu can trigger an urticarial rash in some people. (You ‘react’ to the virus.) A mild viral infection which causes few other symptoms is probably a common trigger of an urticarial rash th
