Reply #5: Contrary to the old belief

[marzipanni]

that hot water spreads poison ivy/oak on your skin, I have found this to be a great relief when itchiness keeps me awake, if its on an appendage: put area with rash under running tap, start out with cool water then let the water run warm to hot until it approaches scalding and you have to remove your hand (foot, whatever). Instant relief that lasts, and it helps dry up the rash.

Here're some more testimonies to this and other treatments-
http://parents.berkeley.edu/advice/health/poisonoak.html.