Officials have noticed increased sightings of the plant called Giant Hogweed. It is found throughout North America, but if you see one, stay away. The sap from this plant will burn your skin and cause painful blisters that last for days, maybe months. Buzzfeed has images of the plant so you can identify it, and some possibly disturbing pictures of what it can do to you. Link
(Image credit: Wikipedia user Farbenfreude)
It's supposed to remove the UV blocking properties from the area of skin that it touches causing painful burns from only a few minutes of being in the sun.
http://www.youtube.com/watch?v=SDwyBWjfFaM
I didn't even think it was real.
Thanks for the link to the images.