This poison ivy knowledge quiz—accompanied by photos of the plant's varied forms—may help you identify this common rash-inducing growth.

Poison ivy's rash-causing compound is found in the plant's roots, stem, and leaves—so coming into contact with any part of the plant can lead to rashes for the 85% of people who are allergic to it.

Poison ivy's rash-causing compound is found in the plant's roots, stem, and leaves—so coming into contact with any part of the plant can lead to rashes for the 85% of people who are allergic to it

Once sold as an ornamental plant, poison ivy can actually look varied—its colors change seasonally from reddish to green to yellow. It typically has three broad, shiny, tear-shaped leaves. But it sometimes may have a different number of leaves, and its edges can be serrated.

Poison ivy's characteristic rash is caused by an allergic response to an oily compound in the plant called urushiol.

Poison ivy's characteristic rash is caused by an allergic response to an oily compound in the plant called urushiol.

Poison ivy can cause rashes year-round since all parts of the plant contain urushiol, the oil that triggers our allergic response.

Poison ivy is projected to be larger and more resilient due to climate change

Elevated atmospheric carbon dioxide boosts the growth rate of the plant and the resulting leaf area. These larger plants contain more uroshiol—the substance most humans are allergic to—and are hardier, recovering from damage more quickly than their smaller counterparts.

Between 10 million and 50 million people in the US develop rashes from poison ivy, poison sumac, and poison oak each year.

Poison ivy can cause rashes any time of the year

This myth-busting article about poison ivy notes that all parts of the plant contain urushiol, the oil that triggers our allergic response, so if you are in the woods in winter you may be still encounter the plant—and urushiol.

Poison ivy's characteristic rash is caused by an allergic response to an oily compound in the plant called urushiol

Chinese lacquer tree sap also contains urushiol, yet the sap was widely used as a lacquer in Asian lacquerware for thousands of years. The word "urushiol" is derived from the Japanese word "usushi," which is the word for the lacquer tree.

Poison ivy will likely become both larger and more resilient due to climate change.

Poison ivy is in the same family as mangoes, cashews, and pistachios—and they all produce oily urushiol in their raw, unprocessed state—but they are typically prepared in ways to avoid causing human discomfort.

Urushiol, the oily toxin in poison ivy, can remain allergenic on clothing for years.

Poison ivy was sent to Europe in the 1600s as an exotic, ornamental oddity, where it was purposefully grown in the English royal gardens at Kew, the Faculty of Medicine in Paris, and a few other locations.

Poison ivy was sent to Europe in the 1600s as an exotic, ornamental oddity

The plants were grown in the English royal gardens at Kew, the Faculty of Medicine in Paris, and a few other locations.

During the French Revolution, a botanist's letter asking about "dear Rhus" (poison ivy) was intercepted, leading authorities to suspect he was conspiring with the Russians.

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Are you burned out? Take this quiz

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Frequently asked questions on immunotherapy

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Drugs 101: An interactive guide

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View the rainbow effect on the waters at First Landing State Park

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View a gallery of diagrams for each volcano type with glossaries

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The UV index measures the sun's ultraviolet radiation risk on a scale of 1 to 11+

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See these 16 pieces of art evoking phobias of snakes, flying, spiders, and more. 

Take a visual tour of past Coachellas

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Neural replays in mice help explain food aversions

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