Health encyclopaedia - Alphabetical Topic List
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Causes of Nettle rash
Acute urticaria is thought to be activated by a trigger that causes a release of histamine and other chemicals from under the skins surface. This causes inflammation and fluid to gather under the skin, causing wheals and the blood vessels to dilate. The trigger is unknown in approximately half of the cases of acute urticaria.
Known triggers include:
- Medicines - an allergic reaction to certain medicines can cause the urticaria rash. These medicines include anti- inflammatory drugs, and antibiotics (especially penicillin and aspirin).
- Foods - many foods have been implicated in this hypersensitive reaction, the most common are nuts, eggs, chocolate, citrus fruits, strawberries, shellfish and food additives.
- Infections - including colds and flu. Also hepatitis B, glandular fever and intestinal parasites have been associated.
- Irritants, causing local urticaria - many things have been implicated including latex, nettles, plants, chemicals and insect bites.
- Other triggers – can include heat, exercise, exposure to cold, pressure and rarely exposure to sunlight.
Chronic urticaria is rarely activated by such triggers, but usually starts as an autoimmune response, where antibodies which usually fight bacteria and viruses, appear to cause histamine and other chemicals to be released under the skin, causing the same response as above. The reason is unknown.
