According to a study published in Weed Science Journal the slight elevation in carbon dioxide levels that we have experienced since the 1950s have caused poison ivy plants to double in size. Not only that, but the itch causing substance "urushiol" is more concentrated these days too. Yikes! Talk about a one-two punch. With all that, it is not a surprise that severe poison ivy induced rashes are on the rise.
Careful when you are out on the trails and if you are not sure you can identify the plant read: Know Your Enemy: Poison Ivy.