|I had a severe case when I was 11 years old. It left scars on my arms.
After that I became immune. The stuff never bothered me again. If I get a very large exposure I might get 1 tiny blister that goes away within 2 days, but even that is rare.
I try not to get it on me or my clothes. With no reaction I don't know I have the oil on me and may cause others to become exposed.
I know some people who seem to get more sensative with exposure. Some even needing hospital treatment. So it is not exposure that leads to immunity I think, but something about individual response.
Glad I am immune now. The case I had at 11 years old was very bad. And I see how bad others suffer.