I have a ton of allergies, but somehow, poison ivy does nothing to me. There was ivy growing on both ends of my house and I would go out a couple of times a year and tear it off and thought nothing about it being PI. A friend bought my house to flip, and he calls me up and says, "Man, I tore that ivy off the walls and have horrible PI!". I was shocked to learn it was PI, but even more shocked to learn that I had been handling it for years with no effect. Plain old grass rubbed on my skin makes a big welt, and pine needles about make me go to the ER. Any kind of real Christmas tree made me feel like I had about the worst cold ever.