In my experience from working in the woods from a young age with my father, I have found that the body can build an immune response to poison ivy. This may seem confusing since the body can also build an allergic reaction to poison ivy. The question is why in some cases is an immune response built and in other cases an allergic reaction is built? My personal feeling, again based on experience and not regulated studies, is that an immune response is built at a young age when the body is building immunities. If the immune response is not built at a young age, through limited contact with poison ivy, the body becomes confused when it encounters it later in life and an allergic reaction is the result.
I say this comes from experience because from working with my father in the woods from the time I could walk I was in limited contact with poison ivy and my brother and I never contracted poison ivy even when we were much more liberally exposed to it in our teenage and young adult years.
Furthermore, from working with other families and work teams throughout my younger years we became to realize that all of the people exposed to poison ivy from a young age in some consistency (i.e. working around it everyday while young) that we encountered also never contracted an allergic response to poison ivy. In contrast, whenever we encountered someone on our work team that had not been exposed to it early in life contracted it almost immediately. This was obvious due to the fact that many of us that were 'immune' would tear down poison ivy and those that were not would avoid it at all costs only to come down with it in any event.
Another twist to this tale is that after graduating from college I moved to the south (Florida and then Georgia) where I worked in an office and was not exposed to it for probably about 7 years. When I moved back to the north I contracted it while working with it in my yard. Up until that point I had never gotten poison ivy. My opinion is that my immune response was confused because it had not been employed for so many years. I also have allergic reactions to pollen in the north that I never had until I moved away and returned many years later. The level of exposure was dramatic in my younger years. In addition to pulling it down and eradicating it on a regular basis working in the woods I also slept in it once when I selected an under the stars camp site on a bike trip. I slept directly in a patch of it on the beaches of Cape Cod (it was quite comfortable actually). The other two people I was with did not sleep directly in it but must have touched it in some fashion because they both came down with an allergic reaction. I did not have any response.
I think this side of immunity vs. allergic reaction is not discussed in the main stream because we as a society feel it is best to just avoid poison ivy and this is the best way to avoid contracting it. Although this may be true, I see it as a fact that if the body is exposed to toxins at a young age in limited amounts the body naturally builds an immune response instead of a allergic reaction. The body will continue this response as long as it is tested on a regular basis. If there is too long of a break from exposure the body may resort to an allergic reaction from a lack of employing the immune response for an extended period of time.
The body builds responses based on the environment they are in. We focus so much attention on allergic reactions that we forget that the body is a powerful force that can also build immune responses. This can be observed in history as well. Anytime you have people that are put into a environment where they are exposed to toxins, diseases, and virus' that they are not accustomed to the body will react in dramatic ways. This is why when the 'New World' was encountered by Europeans there were mass deaths of Europeans from illness that came from the 'New World' and mass deaths of Native Americans from illness brought over by Europeans.
Please let me know what your thoughts are regarding this issue.