The effect may also be seen with closely-related poison oak and poison sumac.

And a CO2-driven vine also produces more of its rash-causing chemical, urushiol, conclude experiments conducted in a forest at Duke University where scientists increased carbon-dioxide levels to those expected in 2050.

Carbon dioxide is a greenhouse gas – a chemical that traps heat similar to the way a greenhouse does – that’s considered a major contributor to global warming. Greenhouse gases have been steadily increasing in the atmosphere since the Industrial Revolution.

Poison ivy is common in woods around the country, making it a bane of hikers, campers, fighters of forest fires, even backyard gardeners. Its itchy, sometimes blistering rash is one of the most widely reported ailments to poison-control centers, with more than 350,000 reported cases a year.

Compared to poison ivy grown in usual atmospheric conditions, those exposed to the extra-high carbon dioxide grew about three times larger – and produced more allergenic form of urushiol, scientists from Duke and Harvard University reported.

Their study appears in this week’s Proceedings of the National Academy of Sciences.

“The fertilization effect of rising CO2 on poison ivy … and the shift toward a more allergenic form of urushiol have important implications for the future health of both humans and forests,” the study concludes.