American native plants include poison ivy, poison oak, and poison sumac. In most cases, those who are exposed to these plants experience an allergic reaction. To become allergic to poison ivy, you must come into contact with the plant just once to cause urushiol sensitization or irritation. After exposure, a reaction might appear 24–72 hours later. By touching the blisters or from the fluid inside the blisters, the reaction from poison ivy cannot be transferred from one person to another. However, if plant oils are left on the skin, clothing, or shoes, it may spread.