This is what I do. Anytime I am out in the woods and I come in contact with it, I make sure I wash all my clothes in hot water, heavy on the detergent. Then I scrub all exposed skin down with dawn and a brush. If I develop a rash, I repeat the process with dawn and a brush. When I do that, it's rare I ever get a rash, and the if I do, rewashing usually does the trick.
If it still won't go away, then prednisone, as someone else mentioned will do the trick.
You have to think of the oil on the plant as tar or grease. It doesn't just wipe off. It doesn't just wash off with a little soap. You have to put some effort in.
