Urticariogenic plants are similar to cacti in that they cause mechanical injury, but they also involve a pharmacologically active toxin and are often tropical as opposed to desert plants. Nearly all plants in this group belong to the family Urticaceae, and the most prolific plants are nettles (Urtica). They contain minute stinging hairs that can inject a fluid containing histamine, acetyl-choline, and serotonin into the skin, causing an immediate inflammatory response characterized by a burning sensation followed by itching. Stings tend to be self-limiting and thus do not usually require treatment (39,41).
Not all urticariogenic plants contain stinging hairs; for example, various urticariogenic fruits, such as kiwi and strawberries, do not. However, kiwi-induced urticaria has been noted as a significant occupational hazard in New Zealand, where the kiwi fruit is a major cash crop (48).
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