Whether its on ourselves or on camping companions, most of us are familiar with the red, itchy rash caused by touching poison ivy. The culprit behind that rash is a chemical called urushiol, which lurks not only on the plant's leaves, but also in its stems, roots, flowers, and berries. What you may not know is that this same chemical is also contained in the skin of the mango fruit, plus the bark and leaves of the mango tree. If you get a reaction from poison ivy or its cousins, poison oak and poison sumac, you may find yourself with an itchy, blistering, swollen lip after eating mango straight off the peel. Luckily, the fruit itself doesn't contain urushiol, so if you slice the fruit from the skin beforehand you'll most likely steer clear of any reactions. Interestingly, cashew shells also contain urushiol, but because they're sold shelled and processed at high enough temperatures to destroy the chemical, they're unlikely to cause problems.