Poison ivy’s shiny green leaves are gourmet cuisine for deer, bear, and other animals. Birds like its white berries and spread the seeds by unmentionable means. But the leaves, berries, and vine are the bane of humankind and primates. In the hours after the lacquer-like oil, urushiol, gets transferred at the slightest contact, mad scratching begins.
Enough urushiol to fit on the head of a pin can cause misery for 500 people. Even a billionth of a gram of urushiol on the skin is said to cause agony. But now the news worsens.
Chances are rising that whitetails and bruins will have plenty of the leafy greens to consume in coming decades, with people facing a growing challenge to avoid the green curse. Climate change is making poison ivy grow faster, bigger, and meaner. Rising atmospheric levels of carbon dioxide and higher temperatures are to poison ivy what garbage is for rats, dormant water is for mosquitoes and road kill is to buzzards.
Opposite of humans and mammals, plants take in carbon dioxide, which photosynthesis converts into carbohydrates, and release oxygen into the atmosphere. Higher CO2 benefits plant growth but especially poison ivy. Pie-pan sized leaves now are common. Poison ivy is choking trees and filling the edge of woodlands.
Lewis H. Ziska, a research weed ecologist with the U.S. Department of Agriculture, said laboratory and field studies show that poison ivy is advancing with climate change. That trend will continue as carbon dioxide levels keep rising from the current average level of about 400 parts per million to 560 ppm or higher in the next 30 to 50 years, with predicted levels reaching 800 ppm by century’s end, he said.
Already poison ivy’s growth and potency has doubled since the 1960s, and it could double again once CO2 levels reach the 560 ppm mark, Mr. Ziska said. As a result, Americans might have to scratch their way into a climate-altered future.
“The chemistry of the oil itself changes in such a way that it more likely will produce a rash when you come in contact with it,” he said. “In the last 50 years, the growth rate of poison ivy plant already has doubled, increasing the risk of being exposed to urushiol.”
Nurturing the enemy
Jacqueline Mohan, an assistant professor of biology at the University of Georgia, participated in the study in which Mr. Ziska and Duke Unversity researchers in 2006 exposed poison ivy to CO2 levels expected to exist within 100 years, proving that the troublesome ivy will thrive and become more potent with climate change.
"Poison ivy and vines in general really, really benefit from higher atmospheric CO2," she said. "Vines use the infrastructure of trees, which means they can use carbohydrates generated from photosynthesis to make bigger, greener leaves."
In her study of forests, she said poison ivy and other vines, including invasive kudzu that botanists statewide are trying to keep under control, can flourish by wrapping around trees and hindering tree growth while the vines take control.
Citing other studies, Ms. Mohan said surveys of forest plants in South Carolina showed poison ivy to be one of only a few plants to be increasing in abundance in coastal plain forests.
"It's getting happier and nastier," she said.
An organic gardener, Ms. Mohan makes poison ivy the sole exception. When she spots it in her garden or around her property, out comes the herbicide. But be aware that even after the plant is dead, or after the urushiol is deposited on a surface, it can remain active for five years, and in some cases, decades.
Why we itch
After working its way under the skin, urushiol is oxidized by an enzyme that allows it to attach to skin proteins. The oil spreads to cause the rash.
Up to 70 percent of people have immune systems that view the modified skin protein as a foreign invader or health threat. The resulting immune response to otherwise harmless urushiol causes the rash, which swells into itchy pimples, which, in turn, can produce large, dome-shaped, orange blisters. Poison ivy can cause five days to six weeks of itchiness.
Rebecca Braslau, chemistry professor at the University of California, Santa Cruz, wrote a grant proposal that details how poison ivy is taking "a huge human and economic toll."
"Contact dermatitis from exposure of skin to urushiol causes agony and suffering for tens of millions of Americans each year and is a significant cause of workers' compensation disability, making this an important human health and economic issue in North America," the grant application states.
Poison ivy also increases medical visits and lost work and school days.
Tecnu soap and Ivy Cleanse are designed to remove stubborn urushiol before a rash begins. Other products prevent urushiol from reaching the skin. Doctors use steroid treatments to calm the itching. Some dishwashing soaps included Dial Ultra can be used to remove urushiol from the skin before an allergic reaction occurs.
But once it does, a person can only try to calm the itch with Calamine lotion, cortisone topical treatments or such treatments as All Stop and Zanfel. Ice can help tame the rash, too. Very hot water on the skin can relieve itching but also can open pores to allow more urushiol under the skin, Ms. Braslau said.
Her UCSC team — the Braslau Research Group — has developed and now is refining a fluorescent compound that will attach to the urushiol to make it visible under a black light, so a person can wash it away before trouble begins.
When the Cherokee were in its vicinity of poison ivy, they would address it as "my friend" to reduce its anger. Batman comic books included Lady Poison Ivy as a formidable foe. Movies, television shows and books have used it in their titles.
Poison ivy, oak and sumac, all spiked with urushiol, are part of American culture, lore and legend due to the profound agony they cause humanity. But Ms. Braslau said the fact animals eat poison ivy indicates that urushiol is an oil that helps the leaf retain water rather than ward off predation. Humans aren't its target.
As Batman found out, poison ivy can be life-threatening. If it is burned and inhaled, it can cause swelling of airways and the linings of the lungs, which can be deadly. Poison ivy can become airborne from weed-whacking and cause body-wide itching. Sleeping with a pet with urushiol on its fur or a night in a sleeping bag that has urushiol can cause a massive rash that could require hospital care.
"There's no getting rid of it," said Cynthia Morton, curator of botany at the Carnegie Museum of Natural History.
"They can give you steroids to calm it down and anti-itch medications that can make it calmer so you don't freak out. But there's no getting rid of it."
She noted other plants that can threaten health, including raw pokeweed that's eaten, and hemlock and jimson weed, which has hallucinogens that can be deadly and causes the highest number of deaths in adolescents of any plant.
But in terms of health emergencies, poison ivy leads the vegetative world, accounting for the most doctor and emergency-room visits each year.
Ms. Morton is working with Marios Savvides of the Carnegie Mellon University Biometric CyLab to develop an app that doctors can use, especially in the emergency room, to determine what plant the person was exposed to or ingested, with expected symptoms and best treatments.
Poison ivy is the most common culprit, but pokeweed, hemlock and oleander have caused their share of emergency room visits.