Poison ivy is the most common allergy in the United States, affecting about 50 million people every year. The rash from poison ivy is caused by an allergic reaction to urushiol, an oily substance in the leaves, stems, and roots of poison ivy, through direct contact. Urushiol is also found in poison oak and poison sumac, which means the rash can be contracted by interacting with any of the three plants. Other than direct contact ...
