Poison ivy contains an oily resin known as urushiol. It’s colorless and odorless, and is found in the leaves, stems, and roots of the plant.
This oily substance easily sticks to many different types of surfaces when it comes into contact with them, including skin, clothing, pet fur, and outdoor tools and equipment.
“If you get it on your shoelace, then you tie your shoe and you wipe your forehead, you could have poison ivy on your forehead,” says Linda Radimecky, an interpretive naturalist at Afton State Park in Hastings, Minnesota.
No one is born allergic to poison ivy, though.
“Our bodies become sensitized to poison ivy after an initial exposure,” says Joshua Zeichner, MD, director of cosmetic and clinical research in dermatology at Mount Sinai Hospital in New York City. “Upon future exposure, our immune system becomes activated, leading to significant inflammation.”
In addition to direct contact and touching contaminated items, you can also have a poison ivy reaction by breathing smoke from the plant if it’s burned.
Poison ivy isn’t contagious unless there is still oil from the plant on your skin and you spread it to other surfaces. You also can’t spread a rash across your body by scratching once you’ve washed off the oil.