i suggest we can only get the rash as a result of having mineral im-balance, mostly iron is my guess...because when people consume plants known to balance iron, the rash dissapears rapidly.
i use to get poison ivy bad and when i got into herbs, it went away.....i have not gotten it for years now.
i make a ivy formula for the amish, because so many are wood cutters and each spring they want 5 gallons.