Wait, Is That Poison Ivy? A Quiz.

"Well over half of the human population is sensitive to poison ivy, poison oak or poison sumac. Rashes usually peak in early summer, and tens of thousands of people in the United States go to the emergency room every year as a result. Even if you've gone your whole life without a sensitivity, you can develop an allergy at any point. Your best bet for staying rash-free is leaving plant life alone."

"A good rule of thumb is leaves of three, let it be. Leaf shape, size and color are less helpful, since they are notoriously varied in these plants. Another important tip: The entire plant, from root to leaf, contains the allergenic oil urushiol. Ready to test your knowledge? That's poison ivy."

"Poison ivy and oak leaves almost always grow in threes, shaped like a lowercase t with two leaves (technically called leaflets) on the sides and one at the end with a slightly longer stem. Fun fact: The allergenic oil is on only the inside of the plant, not the outside, according to John Jelesko, a botanist at Virginia Tech. But best not to press your luck."

"There is plenty of anecdotal evidence that urushiol can stay active on clothes and objects for perhaps a year, though this hasn't been well studied. Your safest bet is to clean the tools with soap and wash any clothes that might have oils on them. Poison ivy, like many plants, changes colors in the fall. And it can give you a rash year round, though there is less oil in dead leaves."

More than half of people are sensitive to poison ivy, poison oak, or poison sumac, and rashes often peak in early summer. Tens of thousands of people in the United States seek emergency care each year due to these rashes. Sensitivity can develop at any point, even without prior reactions. The most reliable identification rule is “leaves of three.” Leaf shape, size, and color vary widely, so they are less dependable. The allergenic oil urushiol is present throughout the entire plant, from root to leaf. Urushiol can remain active on clothes and objects for perhaps a year, so tools and potentially contaminated clothing should be cleaned and washed with soap.

Read at www.nytimes.com