How do i tell the difference between poison oak and poison ivy?

Plant allergy: Poison ivy has leaves of 3 and smooth edges. Poison oak has leaves of 3 and has rough edges like an oak leaf. They both cause blister like rashes to skin.

Compare plants: Poison ivy grows along the ground and up on trees sticking to the bark. Like ivy. Poison oak grows like a bush. The reactions when an allergic patient touches them is similar for both and treated the same.