What is urushiol?

Urushiol is a chemical found on certain plants, including Japanese lacquer trees, poison ivy, poison oak, poison sumac, and mango trees. At room temperature, it is a yellow liquid. It is extremely powerful and potent, and 1 nanogram (1 billionth of a gram) can cause a skin rash in sensitive people. In fact, urushiol specimens which are hundreds of years old can still cause a skin rash in people today! Urushiol is extremely sticky, and can stick to a surface (including clothes and dead plants) for 1 – 5 years. The Japanese use lacquers (urushi, from the Japanese lacquer tree) derived from urushiol, which is where its name comes from.

Outside of East Asia, poison ivy, poison oak, and poison sumac are common. A rhyme used to remind people to leave these plants was “leaves of three, let them be.” Poison ivy and poison oak both have three leaves per cluster, but poison sumac can have between 7 and 13 leaves on a branch. Direct contact with urushiol oil is required to trigger a reaction – but these oils can become airborne in fires, and leaves or fragments of leaves can become airborne during activities such as cutting grass.

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