That stuff is pure torture when you have to work in the heat and humidity. I've learned to wash thoroughly within 2 hours of exposure and it will eliminate it or at least greatly reduce the rash.
I had systemic poison ivy in 2011; I was cutting a tree that had a dead vine on it, the diameter of the vine was about twice the size of your thumb. Since it was dead and I didn't see any moisture coming out of it, I thought it wouldn't still be able to cause a rash. It was July and I was pouring sweat even that early in the morning. I worked the rest of the day and then showered that night. 2 days later I started breaking out on my side where the chainsaw was throwing the sawdust. I continued to break out all over my side, on both arms, neck, face, and in the crease of my leg all the way down to the family jewels! If there is a hell on earth I experienced it. I would wake up at night from scratching it in my sleep until it bled. I continued to get little rashes over the next 2 weeks in random spots: the palms of my hands, the bottom of my feet, and my scalp, places where the oil couldn't have gotten to. The doc said I was exposed to so much urushiol oil that it got in my blood.
FYI: the highest concentrations of oil are in the vines and the oil will remain for years.
It makes me itch just thinking about it.