All plants need the sun in order to grow, but leave it to blister bush to use the sun against you.
Native to the Table Mountain region of South Africa, blister bush, with its greenish-yellow umbrella-shaped flowers, is perfectly harmless. Perfectly harmless that is, until you touch it and an unpleasant cocktail of psoralen, xanthotoxin, bergapten and other chemicals are brushed off the plant's leaves and onto your skin.
In all likelihood, you won't know anything is wrong until two or three days later when a severe, red-purple rash and large burn-like welts appear on your skin. Blister bush's chemical concoction, it turns out, is phototoxic. Exposure of the chemicals to sunlight triggers the reaction to develop from a mild irritation to severe blistering requiring weeks to heal. Luckily, for those hiking in the Table Mountain area, immediately rinsing and covering areas of the skin exposed to blister brush will greatly reduce the severity of the reaction.
Blister bush isn't the only plant that can cause phototoxic reactions. In Wicked Plants: The Weed that Killed Lincoln's Mother and Other Botanical Atrocities, Amy Stewart dedicates a whole section to these sun-loving troublemakers.
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