For years my family and friends have used what everyone calls old fashioned lye soap, this is made with lard only. Seems to help with the poison oak, especially if you wash with it as soon as possible after contact. Some of the older people in the little town where I live swear by it.
Last week after weedeating I came in and showered with the lard soap and I had no effects of the poison oak, although my daughter who wasn't even outside got a rash on her from it. After some investigation we think we figured out how she got it. My dachshunds were running around where I had weedeated, and of course they get in the bed with her at night. A website I was looking at said that dogs can get it on their fur and then transmit it to people.