ocr: Leaves OT three, Tet them be, 1S a ramiliar phrase tor many people, and with good reason. Certain three-leaved plants, particularly poison ivy and poison oak, are probably the most common causes of contact dermatitis. Poison sumac, which has multiple leaves, is a common offender as well. Four of every five Americans become sensitive to these in: some degree. Although the plants are different, the problem- causing substance is the same, an o'ly resin called urushiol. Kl Poison Plants A reaction occurs when o sensitive person comes in contoct with o resin-containing plant (by brushing against th ...