If you’re exposed to poison ivy, avoid scratching at the exposed area, instead use Dawn dishsoap and hot water to clean the exposed/affected area A.S.A.P.
Pop some antihistamines and coat the inflammed area in Calamine lotion.
In cases of extreme itch, use a bag or bags of frozen peas to chill itching skin. It is impossible for the same skin to be itching and cold simultaneously.
The allergen or “poison” part of poison ivy, poison sumac, and poison oak is a clear oil called “urushiol” that coats the respective plants. It transfers relatively easily on contact and can still cause an allergic reaction more than a month later. This makes it difficult to gauge exposure.
All that said, I’ve never had a reaction. A friend asked me to help clear out some poison ivy in his fence line recently. Beforehand, I took a single leaf and rubbed it on the inside of my wrist. There was no reaction, so the next day I ripped out everything I could for my friend.
I suspect there is both a gentic immunity at play and that aquired resistance may play a role as well. My mother was not immune, the rest of us were. ✌