Just some more thoughts on it... Most experts believe that after 30 minutes, the oil (urushiol) from poison ivy and oak can't be washed off; it's too late, and has "sunk" in by that time. So usually, it's too late by the time I get home from a hunt...

Washing with hot water also opens the pores, and can allow the oil deeper into your system... (I've had it internally as well. I've heard horror stories about people who've breathed it and contracted it inside their lungs).