I also 'WAS' one who was not affected by it. I grew up in the woods and I never got it when all the others would. So I thought I was immune. However..hehe..if you read my earlier entry from last month you will see I did get it.
What they ( Dr.'s and experts) say is that there are 2 types--those who react to PI PO PS....and those who 'will' react to it. Seems we have a certain level of resistance...( if you play games ^.^ is sorta like HitPoints) and you may have more resistance to Poison Ivy HP's, hehe... but these HP's are not, "not" regenerating. Once you've run out you are OUT. After that each exposure will be worse. This is from Info I spent hours reading...from medical fact articles not only from word of mouth.
That is why I got it so badly....I knew what it was but 'knew I was immune'. Hehehe, what a nasty joke on me. My 2 son's were also there and were walking through it ...my boyfriend also was exposed but he did attempt to avoid it. only I reacted on this trip. So... it could be that a significant number still have a resistance....since I was the only one of my family to react.
One other nearby camper also got it...all over his... =) ( you figure it out) hehe....he had a bad recovery from the trip too.