The oil in the poison ivy is called urushiol, and that is the oil people are sensitive to. Never burn poison ivy as the oil in the smoke will get into your lungs and can be really bad for you, even cause death.
One sunny day I put on my shorts and short sleeved shirt, and took the weedwacker to a patch of overgrown vines and grass on a local trail. I buzzed and buzzed and got my legs covered with plant matter along with my arms, but my legs were the worst. And then I had a reaction which told me it was poison ivy.
To combat this I used Dawn dish detergent to remove the oil right away, using a warm soapy water and an old washcoloth and towel I could throw away. I certainly did not want the urushiol to get into the washer to taint other clothing. Then I patted down the area to make it dry. Then I found some liquid benedryl to put on the area. I did this about 4x every day, sometimes more at first.
The itching was terrible and I often itched myself until I bled. The redness lasted for about 4 weeks on my legs, the arms cleared up a bit sooner. I also took antihistamines to reduce itching but they never took it all away.
And then I made it my goal to learn all the forms of poison ivy, and differential identification, such as: what's the difference between virginia creeper (where young shoots have 3 leaves) and poison ivy? Well, when it's growing up a tree, poison ivy has many hair-like roots to attach itself to a tree, VC does not. I'm talking about 10-20 rootlets in PI per inch of vine. So find a vine with many hair-like roots attached to a tree, and follow it down to the ground. The PI can also spread on the ground easily. VC also can have 3-5 leaves per terminus, while PI will only have 3. The color of PI can vary throughout the season from light green early in spring to a dark green. But PI tends to have smooth leaves. I never did see any PI that had a white, shiny underside so I do not use that to ID it. WC tends to have more texture as the veins are more indented in the top of the leaf.
Urushiol has been found to be active even when some people found it in 4000 year old Egyptian tombs.