Having had a spouse who would break out in a rash at the sight of poison ivy/oak, I came across a small notation in the back of a chemistry magazine on “home remedies that worked.” This one was a gem and was very inexpensive.
At the first sign of irritation caused by poison ivy/oak, wash the area with soap and water if possible, but in any case, spray (never use a stick or roll-on) the area with an antiperspirant containing aluminum chlorhydrate. Arrid Extra Dry was a favorite, but any kind that is not too sticky will work. Simple deodorants won’t work; it must be an antiperspirant! This material reacts with the urushiol, the principal irritant in poison ivy/oak, and deactivates it. It will even provide relief and start healing when oozing blisters are present. My sons never went camping without it.