The increasing amount of the gas being released may cause poison ivy to grow at almost twice its current pace in the next 50 years, says a report published today in the Proceedings of the National Academy of Sciences.

The study found that poison ivy grew about 149 percent faster in an environment with a higher concentration of carbon dioxide. At the same time, urushiol -- the chemical in poison ivy that causes rashes and sometimes more serious symptoms -- was found to be about 153 percent more concentrated per leaf.

Urushiol is found in the sap of poison ivy, oak and sumac plants. It causes an allergic reaction in about 85 percent of the population, according to the American Academy of Dermatology. The chemical can be transferred to human skin by contact with damaged leaves or by touching other things that have been in contact with it, like garden tools, a dog or clothing. It can be inhaled by breathing the smoke from burning the leaves.

The rash can start as a slight itchy spot but can swell and become large, red blisters. Breathing in urushiol can cause the lungs to swell and accumulate fluid, which can lead to respiratory failure.

"We're normally concerned with carbon dioxide because of climate change," said William Schlesinger, an environmental chemist at Duke University's Nicholas School of the Environment and Earth Sciences and one of the scientists involved with the study. "This is a more direct reason to be concerned. It provides a direct human health impact."

The study, compiled over the course of about six years, tracked an experiment that simulated what scientists think the level of carbon dioxide in the atmosphere will be by 2050.

And they exposed an entire forest -- the portion of Duke Forest off Eubanks Road in Chapel Hill -- to the higher concentration.

During photosynthesis, green plants create energy by absorbing water, sunlight and carbon dioxide to produce sugars and oxygen. With increased carbon dioxide comes more photosynthesis.

Vines are the faster-growing plants in this kind of environment, Schlesinger said Monday, because trees and other wooded plants have to use their photosynthetic energy on their support structure, such as trunks and branches, and eventually into growing new leaves.

But since vines don't have the same structure, their photosynthetic energy goes straight into growing more and more leaves. And each leaf will hold more urushiol.

Since 1959, carbon dioxide in the atmosphere has risen about 20 percent, Schlesinger said. And in the past 10 years, it has risen about 4 percent.

"So you can expect bigger plants and the toxic substance per gram of leaf will be higher," he said.

Does that mean the urushiol will then become airborne?

"There's nothing in our study that says the compound is being emitted as a gas," Schlesinger said. "The only time there is a documented air transfer is if there's a burning poisonous plant [and a person breathes in the fumes]."

He expects the skin rashes to get worse in the future as the poison ivy and the urushiol become more widespread.

"This is a dramatic skin irritant," he said. "It can open up into some really nasty, bleeding sores."

Showering and changing and washing clothes right after contact with the leaves is strongly suggested. Also, wash off all tools after yard work.

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