When I was in fifth grade I was walking home with Steve Sessoms - a sixth grader. We passed a sprawling stand of poison ivy and Steve told me he was going to get out of school. And before my astonished eyes he rubbed himself all over with the leaves of poison ivy.
Poor Steve. He did miss some school and had to be hospitalized. Rumor was they had to tie his hands to the bed to keep him from scratching. Of course I already knew about poison ivy but this was the first time I understood that just because someone was older, they weren't necessarily smarter.
Here in California we have poison oak, not ivy. Both plants contain the same chemical - urisol -- which causes the topical skin reaction in many people. Poison oak belongs to the same family as cashew, mango, sumac and pistachio. I know some people allergic to cashews and mangoes, poor things.
The scientific name for poison oak is Toxicodendron diversilob, which means the poisonous tree with various shaped leaves. This plant can almost be a tree but often occurs as a very large shrub. But it can also be a prostrate vine barely visible among the rocks along the coast or it can clamber more than 100 feet up a redwood. It can thrive in shade or full sun and in a diversity of habitats throughout the West all the way up to about 5000 feet in the Sierra. The leaf shape is also quite variable, sometimes lobed like an oak leaf or with perfectly straight edges even on the same plant.
Breathing the smoke of burning poison oak can be quite serious. Just check with California firefighters. Native animals and domestic pets don't suffer the ill effects like us primates. The chemical probably developed as an antibiotic; it's nothing personal against us humans. We just happen to have a strong response to it.