Some plants contain the same oil (urushiol) found in poison ivy, oak, or sumac, or they contain a substance that is similar enough to urushiol to cause a similar rash. Contact with these plants can make you allergic to urushiol so that future contact with poison ivy, oak, or sumac will cause a rash, even if you never had previous contact with poison ivy, oak, or sumac. These plants include:

• The ginkgo tree.
• The Japanese lacquer tree.
• Mangoes (the allergenic oil is in the fruit's rind and leaves).
• Cashews (the allergenic oil is in the shell).
• The Indian marking nut tree.
• Tropical silk oaks (sometimes grown as ornamental houseplants).