I got a really bad case of
poison oak two years ago, which went systemic, and I had to take
prednisone for quite a while before it got better. Ever since then, if I eat anything with mangos in it, or sweetened with mango juice, I will have a recurrence of a rash in the exact same spots! (Mangos are in the poison oak family.) Also, any kind of skin irritation (I am prone to contact dermatitis as well, and I'm reactive to metal also) may cause those spots to erupt in a rash again.