Ever since I can remember, I have been severely allergic to poison ivy, poison oak and poison sumac. It's an allergy that I dont wish apon anyone. I guess I'm a rare case, because all the books say that the rash won't spread once the oil is completely washed off, but with me that's not the case. I will go to sleep after showering and putting clean clothes on with the rash on just my leg and wake up with it all over my body. 
As you can see from this picture above, the rash even spreads to ny face causing my eyes to swell shut. I'm tell you, it's not a pretty sight. Not only do I look like a monster, the rash won't even start clearing up until about a week goes by, that's with a sterroid shot.
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My advice, STAY PROTECTED.Learn what the different plants look like. If you know your going to be in an area that it can grow (almost anywhere), and either cover your body or steer clear. Always stay far away because I have even gotten it standing near the plant when the wind is blowing. If you know you may have gotten close, wash the body and clothes really well, immediately. The oil from the plant (substance from the plant that causes the rash), no matter where it is ,will still cause a rash even a year later.
Here is some information I found, in hopes it will prevent you from getting it in the future.
Toxicodendron radicans, commonly known as eastern poison ivy or poison ivy, is a poisonous Asian and Eastern North American flowering plant that is well-known for causing urushiol-induced contact ... Wikipedia
Scientific name: Toxicodendron radicans
Rank: Species
Did you know: Bushes of poison ivy are usually 3 feet and 11 inches tall. softschools.com