Poison Ivy 101

An Introduction to Poison Ivy

As a naturalist one of the biggest concerns I run into out in the woods deals with poison ivy, so here's a quick primer.

What type of plant is poison ivy?

Poison ivy (Toxicodendron radicans) isn't really an ivy, like English ivy, which can be confusing. It's actually a plant that has many forms. You can find it crawling along the ground as a runner vine, as a bushy shrub, or climbing trees as a vine. It grows in most of North American, and can usually be found in disturbed areas that are sunny. They particularly spread where humans have been. Which means you'll find poison ivy along road sides, trails, rest areas, houses, etc. Unfortunately poison ivy really likes higher levels of CO2 as well, so as climate changes, it keeps growing!

What does poison ivy look like?

Poison ivy 4

(flicker: Vilseskogen, commons)

Poison ivy has three leaves, so remember the saying "Leaves of three let it be." Usually the leaves range in color from light green (younger leaves) to dark green (older leaves). Sometimes the older leaves have a shiny or waxy appearance. The leaves are usually spear shaped with large teeth, but very little serration on the leaf edges. Where the leaves meet there is a red dot in the center.

Poison ivy 2

(flicker: Afternoon_sunlight, commons)

The vine of poison ivy can either appear as a runner or rhizome along the ground or as a hairy thick vine growing up a tree. Be careful! Both the leaves and the vines carry the oils that can make you itch! Remember, "A hairy vine is no friend of mine!"

poiso ivy vine

(photo: wild plant database http://www.wildplantdatabase.net)

The berries of poison ivy are quite poisonous and are not to be eaten, but they are edible for many species of native birds. Remember, "Berries of white make a very bad night." the picture below shows the green unripe berries and white berries below.

pi berries141

Poison ivy is quite brilliant in fall, so don't be fooled by the colors of the leaves. A close friend of mine was picking beautiful fall leaves and found out the hard way that they were not the good kind to collect. Colors can range from yellow to bright red.


Why does poison ivy cause a rash?

The sap of poison ivy causes the rash. The oil responsible is something called urushiol (ur-rush-ee-all), which binds with skin on contact. These toxins are found in the leaves, berries, vines, and runners of poison ivy so be careful! Even winter vines and fall leaves can have the oils.

How does poison ivy spread?

  • You can spread the oil through contact with clothing, tools, gloves, etc. so it's best to wash after contact.
  • If you have walked through poison ivy, with your ankles/socks you can spread it by dropped shorts or pants, carrying the oil upward (learned from experience), so don't let your knickers brush your ankles if you have come in contact (or think you have)! If you are hiking, then when you return home be sure to turn your clothes inside out as you get out of them and take your clothes off in a "safe" area where they won't come in contact with other clothing or surfaces
  • Urushiol can also become airborne if the vines are cut and burned, so please handle the plant carefully! A lung full of poison ivy will make for a very bad day and could even lead to hospitalization. Weed-eaters can also spray the leaves and vines onto your bare legs, arms, or body, so please don't use a weed-eater to destroy it!
  • Remember that you pets can spread the oils too! By rubbing their fur in the plants dogs and cats can spread the oils to humans. Be sure to keep animals out of areas with poison ivy.


How long does it take poison ivy oils to cause a rash?

Thoughts vary on how long the oils take to soak in, and the rate can vary based on weather and sweating. It can take up to half an hour before the oils soak in in cooler weather but time may be reduced if it's hot and your pores are open. Generally more than an our after contact is too long to wait. Usually the full blown rash takes up to 12-48 hours to manifest.

What do I do if I've come in contact with the plant leaves, vines, or stems?

Wash right away in COLD WATER. Do not use hot water. Cold water keeps your pores closed, where as hot opens the pores and can spread the oils quickly. It's best if you can use some sort of soap, especially soaps made to dissolve the plant's oils, like Technu (http://www.teclabsinc.com/products/poison-oak-ivy/tecnu-extreme). You can also wash your clothes with cold water and soap.

What does the rash look like?

The oils of the plant cause contact dermatitis. This may look like a reddish itchy rash or a single blister like bump. You may also see  line of blisters from where the plant rubbed. If you have wide spread patches, lots of oozing blisters, or a rash on your face or reproductive areas see a doctor right away. This is especially true if you develop a fever.


Do people get more sensitive to the poison ivy oils as they get older?

Yes. Usually younger children and adults don't have as much response to the oils. Over time, after exposure, adults become more susceptible. There are always exceptions and not everyone will respond to the oils, but many do, and sometimes severely.

What can you do for poison ivy rash?

You can treat poison ivy rash with over the counter medications, such as Technu ointment or cortisone creme. If the rash is severe a doctor may prescribe a stronger steroid or ointment, or even antibiotics if you get a secondary skin infection.

For those wishing to go the natural route you can try an application of crushed jewel weed stems, a soak in apple cider vinegar or lemon juice to destroy the oils, or an oatmeal bath to soothe the itch. Aloe Vera may also alleviate the itch. I've found clay to be quite good at drying out the rash, as is baking soda. Remember to let the rash breathe and dry out as much as possible. Don't let it get moist or hot in a covered bandage.

The rash usually lasts about three weeks.

Does the fluid from poison ivy blisters spread the rash?

According to WebMD and Mayo Clinic the fluid does not. Their studies indicate that the leaf oils are very persistent, and stay on the skin for a long time. Contact with the infected area spreads the oils, it's not the fluid blisters that are spreading the infection.

How long does the oils last on tools and implements?

The poison ivy oils do not break down quickly, and they may remain on tools, gloves, sleeping bags, tents, or clothing for a long time. Be sure to wash anything that has come in contact immediately. An application of alcohol helps, especially on shoes or boots. For tools you can use a water hose.

If your pets come in contact with the oils you can wash them in cool water with dish washing gloves to avoid spreading the oils on yourself.

What is the difference between poison ivy and poison sumac or poison oak?

The short answer is that all three are in the Toxicodendron family and will cause a rash.

Poison sumac (Toxicodendron vernix) is less common than the others, found mostly in the Eastern US, and it looks similar to poison ivy. It only grows as a woody shrub or tree and not a vine. The leaves are spear shaped and compound (like walnut leaves) so there are more than three leaves on each leaflet.

Andy Jones, Cleveland Musum of Nat. History

(Photo, Poison Sumac: Andy Jones, Cleveland Museum of Natural History)

Poison Oak (Toxicodendron pubescens) is very similar to poison ivy (with three leaves) except that the leaves resemble white oak leaves, with rounded edges, and they are hairy. Like poison sumac it only grows as a shrub, not a vine. Where the three leaves meet there is a reddish tinged center, much like poison ivy.

Mathew Robinson, Flicker

(Photo, Poison Oak: Matthew Robinson, Flicker)

Where can I learn more?

There are several good books out there, such as:

  • The Poison Oak and Poison Ivy Survival Guide by Sandra J. Baker.
  • A Field Guide to Poison Ivy, Poison Oak, and Poison Sumac: Prevention and Remedies, a Falcon Guide.
  • Nature's Revenge: The Secrets of Poison Ivy, Poison Oak, Poison Sumac, and Their Remedies by Susan Carol Hauser.