You get it because you don’t know how to get it off of your skin.
Let’s back up a bit. You’ve probably all had poison ivy at least once. You’re out in the woods having a great time. You get back to camp and it starts. That wretched itch. It’s terrible. It feels like it’s coming from the marrow in your bones and nothing you do seems to help.
How do you get it in the first place?
Poison ivy has urushiol oil on it and it’s potent stuff. Just one billionth of a gram is enough to cause a rash. Urishiol is also a very stable oil. It could literally be on an axe handle for several years and still be able to cause a rash. Apparently a museum even had 50 year old poison ivy samples that still caused a rash. It’s nasty stuff. The rash generally shows up 8-24 hours after contact.
Soap won’t save you.
According to research scientist Jim Brauker, soap alone can’t remove urushiol oil. The trick is abrasion. You can actually rub off poison ivy. If you’ve ever had to wash grease off of your hands, you’ve seen how this works. Soap doesn’t do a very good job getting grease off, but a bit of effort with a course rag works wonders. Jim says that the same is true of poison ivy. Only aggressive scrubbing with course brush or cloth will remove urushiol oil. You have two to eight hours to remove the oil. Diligence is key here. As you can see in the video below, it likes to hide out in the cracks of your fingers so it can drive you crazy later. Overdo it. You’ll be glad you did.