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"Can you lose a natural resistance to poison ivy as you get older?"
When I was a kid, I never got poison ivy, even when my brother or friends would get a bad rash and we had been playing in the same brushy areas on the farm where I grew up. My Mom was also very susceptible and had to be very careful or she would get a horrible painful rash, but my Dad never was affected, and I seemed to have inherited his natural resistance. I never tempted fate by rolling around in poison ivy on purpose, but felt lucky that I didn't have to worry about it. I'm now 45, and I recently went on a walk in the woods with my dog, and now I have a rash on my leg that I'm pretty sure is poison ivy, probably contracted from my dog running around in the underbrush and then rubbing against me. Do some people really have a resistance or immunity to poison ivy, and if so, can it wear off as you get older?
There is actually no such thing as immunity to poison ivy. Poison ivy rash is caused when a particular irritating, toxic chemical in the poison ivy gets on the skin and stimulates an inflammatory reaction by certain immune cells in your body, called a delayed hypersensitivity reaction. The chemical in poison ivy will produce this inflammatory reaction (and the consequent rash, blistering and itching) in everyone exposed to the chemical, assuming that the exposure reaches a certain threshold. What is true is that some people have much lower thresholds for getting the rash, and so they will seem to be "sensitive" to poison ivy, while other people will have higher thresholds, so they will seem to be "resistant" to the rash. However, a "resistant" person will get poison ivy if they come in contact with enough of the plant for long enough. Another thing that can happen is that repeated exposures over the course of your life can gradually sensitize your immune cells to the chemical. This means that you may appear to be "resistant" for most of your life and then, suddenly with one final exposure, become "sensitive." If you do have poison ivy, talk to your primary care doctor about treatment options.
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