From Our 2007 Archives

Climate Change Brings Super Poison Ivy

Researches Say Boost in Carbon Dioxide Has an Itchy Impact

By Kathleen Doheny
WebMD Health News

Reviewed By Michael W. Smith, MD

Climate change isn't just increasing outdoor temperatures and warming up the oceans. It may also greatly increase your chances of getting a really bad case of poison ivy.

As the level of carbon dioxide in the atmosphere increases, it's boosting the growth of poison ivy plants, two recent studies show. These elevated carbon dioxide levels are creating bigger, stronger poison ivy plants that produce more urushiol, the oil that causes the allergic reaction and miserable poison ivy rash. The urushiol isn't just more plentiful; it might also be more potent.

"Initial data suggests that there may be a more [powerful] form of urushiol being produced with increasing carbon dioxide," says Lewis Ziska, PhD, a weed ecologist at the U.S. Department of Agriculture in Beltsville, Md., and a co-researcher of both studies.

In the last 50 years, Ziska says, the growth rate of the poison ivy plant has doubled. "The chances of encountering poison ivy and coming down with a rash are greater than they used to be," he tells WebMD.

About 80% of people are sensitive to the plant -- meaning they may develop a poison ivy rash if they come in contact with the plant. While the reaction is not typically serious, getting poison ivy can doom you to a week or more of miserable itching. The poison ivy rash can also raise your risk of getting a potentially serious skin infection from scratching your skin. Here's what you need to know before you head out to the woods, or the backyard.

Poison Ivy Studies

In Ziska's latest study, published in the July-August issue of Weed Science, his team compared the effects of four different concentrations of carbon dioxide on poison ivy plants, working in the laboratory. The carbon dioxide concentrations corresponded roughly to those that existed during the middle of the 20th century, the current concentration, and the concentration predicted for 2050 and 2090.

"What we found was even during that 50- or 60-year period that poison ivy could significantly respond to even a small change in carbon dioxide," Ziska says. The growth rate doubled, he says.

Ziska says his latest study confirms the findings of an experiment reported last year in the Proceedings of the National Academy of Sciences. In that study, Ziska and researchers from Duke University and other institutions compared poison ivy plants grown in ambient air with those grown in areas with a piped in system that increased the carbon dioxide levels. In the six-year study, the scientists showed that elevated carbon dioxide boosts the growth of poison ivy and results in the production of a more powerful form of the urushiol.

From Oil to Rash

The urushiol found in the sap of the poison ivy plant binds to skin cells when it comes into contact, says Ziska.

Touching the sap of the plant as well as touching something on which urushiol is present, such as garden tools, can result in an allergic reaction, according to the American Academy of Dermatology (AAD). Burning poison ivy plants can release urushiol particles into the air.

When the oil gets on the skin, it can penetrate in minutes, according to the AAD.

"Once it is absorbed, there is not much you can do," Ziska adds.

"Most people don't know they have come into contact until hours later or even longer, when they start reacting," says David Peng, MD, assistant professor of clinical dermatology at the University of Southern California Keck School of Medicine, Los Angeles. He runs the contact dermatitis clinic at USC, and poison ivy rash is a kind of contact dermatitis.

Typically, there is itching, redness, swelling, and the rash, according to the AAD.

"It can take hours to days to exhibit the rash," says Ronald Brancaccio, MD, clinical professor of dermatology at the New York University School of Medicine and a practicing dermatologist at the Skin Institute of New York. A reaction usually occurs within 12 to 48 hours, the AAD estimates.

Pre-emptive Poison Ivy Plan

Since the poison ivy rash can take its time in showing up, experts recommend a pre-emptive strike approach.

"If you think you have come into contact, wash the [oil] off first, using rubbing alcohol," Peng says. Then use plain hot water. Then use soap and hot water. Discard the soap, and wash the washcloth."

Brancaccio says it's good enough to wash with plain soap and water of any temperature and OK to skip the alcohol and plain water steps.

If you're out on a hiking trail or camping, use cold water from a stream or other source, the AAD recommends, and the sooner the better.

Once you've washed the oil off your skin, you are not contagious and cannot give the poison ivy rash to someone else.

All experts agree on one point, however: launder the clothes you wore when exposed to the poison ivy as well as tents and other camping gear. The oil can stick to clothing and re-expose you.

At-Home Poison Ivy Treatment

If you develop a poison ivy rash despite trying to wash the oil off your skin, you can turn to home treatments to soothe the itching. Apply cold compresses, Brancaccio advises, and then calamine lotion. You can also take Benadryl (available over the counter) by mouth to help calm down the allergic reaction. Be aware that Benadryl pills will likely make you sleepy -- not such a bad thing if you're itching to death.

Hydrocortisone cream, 1% strength, over the counter, can also help.

Poison Ivy Treatment: When to Seek Professional Help

A typical case of poison ivy generally subsides within a week or so, says Wally Ghurabi, MD, chief of emergency services at Santa Monica-UCLA Medical Center and Orthopaedic Hospital in Santa Monica, Calif.

But not always. If your poison ivy rash and discomfort seem to get worse, it may be time to see your doctor or even go to your local emergency department. "When you see increased redness and swelling, when the area is warm to the touch and the rash is spreading, go to the doctor," Ghurabi says.

Difficult as it is, do not scratch the area, he adds.

Ghurabi has seen emergency department patients with widespread poison ivy rashes. Depending on the body part exposed to the oil, the rash can get very uncomfortable, he says. Sometimes, a secondary infection can set in, he says, and things can turn serious, such as a bloodstream infection requiring hospitalization.

Prevention Plan

Avoiding poison ivy is the best bet, researchers agree. "Leaves of three, let it be" is the motto repeated by the experts. Each leaf of the poison ivy plant has three leaflets.

An over-the-counter product containing bentoquatam (IvyBlock) is effective, according to Peng, if applied before exposure. It literally provides a physical barrier, he says, so the oil can't penetrate the skin.

Wearing long pants and long-sleeve shirts, though not always plausible in the summer heat, is also recommended, as well as wearing socks and shoes to garden.

SOURCES: Lewis Ziska, PhD, weed ecologist, U.S. Department of Agriculture, Beltsville, Md. Ziska, L. Weed Science, July/August 2007; vol 55: pp 288-92. Wally Ghurabi, MD, chief of emergency services, Santa Monica-UCLA Medical Center and Orthopaedic Hospital, Santa Monica, Calif. Mohan, J. Proceedings of the National Academy of Sciences, June 13, 2006; vol 103: pp 9086-9089. David Peng, MD, assistant professor of clinical dermatology and director of t he contact dermatitis clinic, University of Southern California Keck School of Medicine, Los Angeles. Ronald Brancaccio, MD, clinical professor of dermatology, New York University School of Medicine; dermatologist, Skin Institute of New York; fellow of the American Academy of Dermatology. American Academy of Dermatology.

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