Don't listen to these kids, the oil the plant secretes will cause the rash. if you itch while the oil is still on your skin you will spread it, but after you've taken a shower (cold water works better) and all the oils are washed off the rash won't spread.
as for the itch, use a hair dryer on the hot as fuck setting and aim it on your rash spots, hold it there until it burns with the scorching heat of a thousand erupting volcanoes, then take it off and let it cool down. repeat until satisfactory numbness of the area is achieved. not only does it feel great but it drys out the rash as well.