About all my life I was little bothered by poison ivy.
I regularly pulled vines from trees in placing stands, and typically only washed my hands hours later. Commonly had some small breakouts, kind of like what BSK described along a scratch line.
Then about 3 years ago, I barely touched some, although I possibly inhaled some poison ivy "dust" from a large dead vine, and it nearly put me in the hospital. I pulled a dead vine off the side of a tree, and this "dust" filled the air, which I breathed a little of it before realizing. A couple days later my whole upper body was one big whelp, and one big itch. But I've had nothing but minor stuff since.