Poison Ivy, Poison Oak, Poison Sumac

By Bob Dispenza, Park & Education Manager, Allen County Parks

Leaves of three, let it be.
Berries white, poisonous sight (or danger in sight).
Hairy vine, do not climb (or no friend of mine).

On nearly every hike I lead I get ample evidence that poison ivy is one of our most misunderstood plants. There’s lots of folklore concerning our favorite rash-causer, but not all of it is true. Let’s take a closer look at poison ivy and it’s “partners in crime,” poison oak and poison sumac.



Recent immigrants and early settlers in America frequently suffered from itching and blistering, but did not know the cause. Poison ivy has been causing itches since Europeans moved to America, and possibly even before. Native Americans are no more immune than any other Americans.

Allergic contact dermatitis is the name medical professionals use for a poison ivy reaction. Rashes due to poison ivy depend entirely on the immune system of the affected person. Some people always get poison ivy, some never get it. Some don’t get it when they are young, but do when they get older (like me). Some could eventually grow out of it. Around 80 to 90% of adult Americans are sensitive to poison ivy oil. It all depends on whether your immune system recognizes the plant’s sap oil and reacts to it like it would to an invading virus or bacteria. The oil soaks into the skin and attaches to cell membranes, which signals the body’s immune system to attack. All the blistering and cell destruction are from the body’s own defense system overreacting to this harmless oil (called urushiol). Since the same chemical causes the reaction, any differences in rashes comes from individual immune systems - you can’t tell a poison ivy rash from one caused by poison oak or poison sumac. Very allergic people may get a reaction from handling Japanese lacquerware, since the glaze is made from a local relative of our poison sumac.

Urushiol (from “urushi,” the Japanese name for lacquer made from sap resins of the Japanese lacquer tree) is found in the resin canals of the plant. It can only come to the surface when the plant is cut or bruised. The oil is very durable, and even long-dead plants can cause a rash.

Urushiol chemical composition:



You can’t get poison ivy just by standing near it. The oils that cause the rash are non-volatile, and don’t evaporate into the air. But if poison ivy is burned, the oil clings to soot and smoke particles and can cause serious illness if inhaled. If you are sensitive to poison ivy and you get it on your clothes or your pet runs through it, you can get the oil on you without directly contacting the plant.

There are many home and folk remedies, most of which have not been proven to work. Some modern “cures” include Neutrogena Oil-Free Acne Wash, Boletus and Polyporus mushrooms (apply freshly-cut surfaces to exposed area) and Ivy Block (which contains absorptive clay). Other less-effective possibilities include jewelweed (wild impatiens, touch-me-not), washing with a strong soap, and applying rubbing alcohol. As usual, the Internet is full of information (and misinformation). Serious cases will need a doctor’s care and stronger medicines. An ounce of prevention is worth a pound of cure – learn what it looks like and stay away.




While the “leaves of three” rhyme is useful, many other plants also have three leaves – young box elder maples, raspberries, and bean and pea relatives. The five-leaved harmless Virginia creeper, which grows in the same places and the same way as poison ivy, is often mistakenly called poison oak.

There is some difference of opinion on what poison oak is. It is definitely found in west coast states, where it grows as a shrub. Some sources also include the southeast US, though many other sources classify the southeastern variety as poison ivy. Either way, poison oak does not occur in Indiana. Yes, I know your doctor or relative told you that you got into poison oak. But it’s just not here.

Poison sumac is a small tree that grows only in bog situations, usually in standing water, and has white berries. You can see it at Pokagon State Park near Angola, IN. Our other native sumacs (staghorn and smooth) are not poisonous and have red berries.

Unfortunately for us, people are the only ones to get the rash. None of our native animals do, and may of them eat the leaves or berries. We don’t actively remove poison ivy in our parks (unless it falls across the trail), since it is an important part of our natural ecosystem.

So, enjoy your visits to Allen County Parks, but take some time to know what poison ivy looks like. Staying on the trails will minimize contact. Like I tell our visiting school children, it’s only a plant, and doesn’t reach out and grab you.