It’s not your imagination: Poison ivy, that pesky summer scourge that can ruin even the most innocent wilderness outing by giving you a nasty case of oozing, itching blisters, is becoming more virulent. With the changing climate, the growth of these hardy vines has been turbocharged by warmer temperatures and rising levels of carbon dioxide (CO2), making them behave like they’re on steroids.

And the CO2-enhanced poison ivy produces an even more potent form of urushiol, the oily sap that causes those itchy rashes, which means that people who are sensitive to poison ivy could develop even more severe reactions.

While state health departments don’t keep tabs on how many people are bedeviled by these annoying rashes, emergency room visits for poison ivy and skin rashes nearly doubled over a 10-year period, between 2002 and 2012, jumping from 472,000 to 929,290 visits annually, according to a study released in 2016.

About 85 percent of the population is allergic to poison ivy (and its cousins, poison sumac and poison oak), and it is the most common allergic reaction in the United States, affecting as many as 50 million Americans each year, according to the American Skin Association.

“As CO2 levels continue to climb, the problem has escalated,” says Lewis Ziska, PhD, a plant physiologist with the U.S. Department of Agriculture (USDA). “Because of warming temperatures, we’re seeing a northward expansion of these vines into places like Canada.”

How Climate Change Fuels More Toxic Poison Ivy

While carbon dioxide is a basic greenhouse gas, it’s also a driver of photosynthesis, acting as a food source for plants, which convert it into sugars and carbohydrates. But not all plants respond the same way, and noxious weeds and vines like poison ivy or kudzu react much more strongly to higher CO2 than other types of plants. As a consequence, we’re seeing not only more growth — many report finding poison ivy vines that are as thick as someone’s wrist — but also more virulent chemicals within the plants.

In a 2006 study, a team led by Duke University researchers pumped extra CO2 over three plots in a North Carolina pine forest. Over a six-year period in a CO2-enriched environment, poison ivy grew larger leaves and produced a more toxic form of the sap oil, urushiol, that causes the allergic reactions. Researchers found that while the average tree grew about 8 percent faster in the CO2-enriched area, poison ivy sprouted 149 percent faster than it would have under normal carbon dioxide conditions.

That’s because of photosynthesis. Trees use up some of the carbohydrates building their support structures, such as trunks, bark, and branches. But vines don’t waste their energy, and use trees, fences, and other structures for support, enabling them to grow more leafy surfaces. This allows them to consume more CO2, making more plant food, which then creates more CO2-absorbing leaves, in a continual positive feedback loop.

“The vines are getting bigger and nastier,” says Jacqueline Mohan, PhD, an associate professor in the Odum School of Ecology at the University of Georgia in Athens, who was also involved in the 2006 Duke study.

Giant Poison Ivy Vines Threaten Forests

The overgrowth of these woody vines is changing the delicately calibrated plant dynamics in the forest.

“When you suddenly change the resources — light, water, food — not every plant species responds the same way, and you’ll have winners and losers,” says Dr. Ziska. “In this case, with the increasing abundance of poison ivy, the woody vines begin to take over and cause increased tree mortality and reduced tree regeneration in the forest.”

Over the long term, this could threaten forests, which could become overrun by these vines, which are already climbing to the top of forest canopies. More recent research conducted by Dr. Mohan, which is as yet unpublished, looked at the effects of warmer weather on poison ivy, and her preliminary results are even more ominous.

“I’m finding that higher temperatures stimulate growth of poison ivy, perhaps even more so than higher CO2,” says Mohan. “This synergistic combination favors vines over trees. We’re already seeing increased abundances of these wooden vines. In both North and South America, whether you’re in the Amazon or South Carolina, we’re seeing big trees being overtopped and choking on these vines. This has bad implications for regeneration of forests in the future.”

Who’s at Risk From Supercharged Poison Ivy?

Anyone who works outside, gardens, hikes, or enjoys the outdoors can be exposed to poison ivy, poison oak, or poison sumac. Even indirect contact, through touching tools, animals, or clothing with urushiol on them, or even inhaling particles containing urushiol from burning plants, can cause an allergic reaction.

In recent years, U.S. Forest Service rangers have reported worsening job-related injuries from inhaling poison ivy–laced smoke, according to a 2007 USDA report, which notes that wildland firefighters and forestry workers run the risk of exposure.

How to Protect Yourself

To avoid touching poison ivy, learn to recognize it. Poison ivy is now endemic to all states in the continental United States, growing in fertile soils below 4,000 feet in elevation. It may be a climbing vine or a woody shrub with three leaflets per stem. These plants can be found in forests, fields, wetlands, and along streams, roadsides, and even in urban areas such as parks and backyards. In the western region, poison ivy leaves have serrated edges, while in the eastern United States the leaves are smoother.

When you're outside where you might be exposed, wear long sleeves, long pants, boots, and gloves. While there are no existing therapies to prevent an allergic reaction, barrier skin creams, such as lotion containing bentoquatum, can offer some protection.

Wash tools thoroughly after use with rubbing alcohol or soap and lots of water — urushiol can cling to the surface of objects and remain active for years — and wear disposable gloves.

“Familiarize yourself with what poison ivy looks like from images on the internet and then avoid it,” says Rebecca Baxt, MD, a dermatologist in Paramus, New Jersey, and a spokesperson for the American Academy of Dermatology. “Shower as soon as possible when you get home using soap and water. If you see poison ivy near your home, spray it with weed killer, but from a distance.”

Prevention and Treatment for Poison Ivy

If you think you’ve been exposed to poison ivy, immediately clean the skin with rubbing alcohol, poison plant wash, or dishwashing soap (which is a degreaser that sops up the sap oil), and plenty of water. Rinse well with water and scrub under the nails with a brush to prevent the further spread of urushiol.

Washing skin quickly after exposure to urushiol can prevent or minimize a reaction to it.

Symptoms of a poison ivy reaction include a red rash, swelling, itching, bumps, patches, or weeping blisters.

Wet compresses, calamine lotion, or hydrocortisone cream can help reduce itching and blistering. Over-the-counter antihistamines can also provide some relief for itching.

If you’re experiencing a rash on your face or genitals, it’s advisable to seek medical attention. In rare instances, if a severe allergic reaction causes swelling or difficulty breathing, go the hospital emergency room.

“As a child grows into adulthood, the severity of the rash generally lessens,” says Meghan Feely, MD, a dermatologist in New Jersey and New York City and a clinical instructor in Mount Sinai’s Department of Dermatology. “But some adults who never had an issue in childhood may develop a sensitivity to poison ivy.”