Research: Leaves of three? Let ’em be

Print Article The three-leaf poison ivy plants such as these are best avoided.

As North Idaho’s wilder areas teem with huckleberry seekers and other visitors, so does an occasional unwanted guest hiding among the wildflowers. Be on the lookout for poison ivy; climbing temperatures make the itchy weed grow bigger and faster.

Using the basic principle that carbon dioxide in the atmosphere fosters plant growth, a Duke University study published by the National Academy of Sciences compared poison ivy grown in historically normal atmospheric conditions with ivy grown in an enhanced-CO2 atmosphere. Not surprisingly the enhanced-CO2 ivy grew faster, bigger, and itchier. One of the conclusions reached was that as average global temperatures increase, so will poison ivy.

Carbon dioxide is a greenhouse gas — a chemical that traps heat like a greenhouse — and considered a major contributor to climate change. Greenhouse gases have been steadily increasing in the atmosphere since the Industrial Revolution.

Poison ivy’s contagious, rash-causing chemical is called urushiol (derived from the Japanese word for lacquer). It’s commonly found in wooded areas such as ours, often encountered by hikers, campers, firefighters and even gardeners. While only one nanogram of urushiol can be an irritant, a typical encounter involves 100 ng. Its itchy, potentially blistering rash is one of the most widely reported ailments to poison-control centers. This ivy plant is rather attractive, so don’t be fooled by its beauty. Its leaves can red, green or both, with three leaves per stem. So remember, “leaves of three — let them be.”

Using soap right away helps, along with over-the-counter and prescription remedies. Most cases last up to two weeks and are benign, but if symptoms (rash, swelling) first appear in four to 12 hours instead of the normal 24, seek medical attention.

For more information on poison ivy and other noxious plants, see


Sholeh Patrick is a columnist for the Hagadone News Network with no compulsion to frequent forests on a hot day. Contact her at

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