"The rash that Poison Ivy causes humans is from the sap, which has an oil called "urushoil" in it. Urushoil only comes out of the plant where it is damaged; however, Poison Ivy is very fragile and breaks easily. Wind, animals, or chewing insects can cause urushoil to be released. When urushoil gets on your skin, your skin absorbs it slowly. Your skin will then have a reaction, resulting in a red rash with blisters. If urushoil gets on your dog or clothes, it can later transfer to you! If you burn wood with Poison Ivy vines on it, the smoke will carry the oil to your lungs, and a trip to the hospital will probably be necessary. Not everybody is allergic to Poison Ivy, and some people are more allergic than others. If you know you've been exposed, wash the area with cold water as soon as possible. Hot water opens your pours so the oil can enter easier."
http://kynaturalinquirer.blogspot.com/2011/05/leaves-of-three.html
