Poison ivy is an allergic contact rash caused by the urushiol oil from sap of poison ivy, oak and sumac. This occurs by touching the plant, or touching something that has this oil on it like a pet or tool. The rash usually occurs within 12-48 hours after contact but may take two weeks to occur. Approximately 85% of people have poison ivy allergy. Poison ivy rash cannot be spread to another area or person unless the oil is spread. Urushiol oil can be eliminated simply by washing. The rash is best treated by prescription corticosteroids early in the course of the rash in addition to cool soaks and topical medications.