Island Science

Itchy & Scratchy: Poison Ivy

by Dr. Sarah D. Oktay
Managing Director UMass Boston Nantucket Field Station

Poison IvyThere are so many things to love about Nantucket that I kind of hate to even bring up anything that isn’t awesome about the island. But there is one thing I do hate about the island, and that is its extremely large and healthy crop of poison ivy. I have had several run-ins with poison ivy already this year. And every year, when I think I may escape it, it crops up again.  It is a common occupational hazard for the island’s landscapers, conservation scientists, botanists, and outdoor enthusiasts. Learning what it looks like and how to avoid it or treat it quickly will ensure you have a great summer.

The Latin name for eastern poison ivy, Toxicodendron radicans, was bestowed by the German botanist Otto Carl Ernst Kuntze. Kuntze was originally an apothecary who did well in his first career and used his earnings to travel the world, collecting 7700 botanical specimens and obtaining his doctorate degree. Kuntze published a three-volume treatise, Revisio Generum Plantarum in 1891 which was widely rejected or deliberately ignored because he proposed radical changes to the rules of taxonomy (binomial system of naming organisms). Poison ivy is not a true ivy which are members of the Hedera genus. Toxicodendron means “poison tree” while “radicans” is derived from the Late Latin word radicare to “take root or grow roots.”

All species of Toxicodendron are equally toxic. Juices and all parts of the plants are toxic year round. Most people have an allergic reaction to poison ivy, becoming sensitized by repeated exposure. The reaction is a contact dermatitis, with a severe form consisting of weeping open blisters [yay, that would be my reaction, which has put me into the ER twice]. The more severe reactions require treatment by a physician, while milder ones can be treated with over-the-counter medications such as caladrel lotion and various drying compounds. The offending agent in the plant is the chemical urushiol. Its name comes from the Japanese word “urushi,” meaning lacquer. Urushiol is the same substance that triggers an allergic reaction when people touch poison oak and poison sumac plants. Poison ivy (Toxicodendron radicans), Eastern poison oak (Toxicodendron quercifolium), Western poison oak (Toxicodendron diversilobum), and poison sumac (Toxicodendron vernix) are all members of the same family: Anacardiaceae. Anacardiaceae (the cashew or sumac family) are a family of flowering plants bearing fruits that are drupes and in some cases producing urushiol, an irritant.  I bet you never would have put both poison ivy and cashews in the same family.  Fortunately, when it comes to poisonous plants, we only have poison ivy and perhaps a few poison sumac (some disagreements in the texts of various botanists) on Nantucket. It is relatively easy to accidentally confuse poison ivy with the very prevalent Virginia Creeper, which has 5 leaves.

In this case, the old adage “leaves of three, let it be,” is true.  Poison-Ivy is perhaps our most common native woody vine. It can grow as a trailing vine, a climbing vine, or as ground cover or a shrub or bush. All parts of the plant cause severe skin irritation in most people. Emerging leaves are reddish. It is quite ornamental in fall, too, when the leaves turn brilliant shades of red and orange. The leaves have three leaflets and are arranged alternately on the branches. Poison ivy leaves are often shiny, bright-green and are compound leaves (two or more leaves on the same stalk). The edges of the leaves usually have large indentations at irregular intervals. The leaves occur in threes, with one leaf at the end of the stem, and two leaves opposite each other on the stem. One distinctive feature to look for is that the central petiolule (the stem leading to the central leaf) is longer than the adjacent petiolules. The hairy aerial rootlets, which often can be seen adhering to tree trunks, are distinctive and help identify poison ivy in winter. Petiole bases are often red. The leaf buds are naked (lacking scales) and covered with short tawny hairs. The small greenish flowers are followed by tawny-whitish fruits (drupes), which are a favorite food of birds.  Aha, so there is a reason to have poison ivy, like many other things humans find a nuisance, it provides cover and sustenance for birds. Eastern poison ivy is distributed across the United States except for Alaska and Hawaii and the Western and Southwestern States; a map of its distribution can be found online at There are seven subspecies that are closely related.

Poison ivy, like all plants in the cashew family grow lavishly in almost all areas of the U.S. and in southern Canada.  The only places you won’t find poison ivy are deserts and areas of extreme heights (> 1500m).  Poison ivy can be found in a variety of habitats and it especially likes edge habitats on the edges of forests and fields because they are not completely shade tolerant.  The plant can grow in woods, fields, city parks, and gardens. They persist in wet and dry climates, and also abutting the ocean.  They have a tough outer cuticle for protection and to retain water which helps it tolerate dry conditions, salty seashores like Nantucket and sun.  A strong, substantial root system makes them very hard to get rid of.

About 85 percent of people are allergic to the urushiol in poison ivy, according to the American Academy of Dermatology. Only a tiny amount of this chemical — 1 billionth of a gram — is enough to cause a rash in many people. Some folks who boast that they are immune have simply not been exposed enough times, it may take several exposures before a rash is developed and people tend to become more sensitive to urushiol over time. But when urushiol from the poison ivy plant touches the skin, it instigates an immune response, called dermatitis, to what would otherwise be a harmless substance. Hay fever is another example of this type of response; in the case of hay fever, the immune system overreacts to pollen, or another plant-produced substance. The appearance of the rash may be delayed by a few days after exposure in some people so that it may be difficult to figure out the cause of the reaction.  The best way to avoid a rash is to avoid the plant and when you can’t do that, where long pants and long sleeve shirts, wash hands after taking off your shoes, and use a product like Ivy Block which uses bentoquatum to from a protective barrier. In the field or in your car it is a good idea to have something like Technu which helps to strip the organic oils off your skin and many companies like Burt’s bees make PI removing soap.

Here’s what you do if you become aware that you have brushed against poison ivy or perhaps touched your pet after they have been exposed to it (it doesn’t bother dogs or cats). First, rinse off your skin immediately with water; rinsing within the first five minutes of contact is most effective. Next, wash thoroughly for several minutes with regular soap and water. If you are hypersensitive, like I am, I would recommend using Technu (after the soap and water step), rubbing it in and leaving it on for a few minutes before rinsing it off, then you may want to use isopropyl alcohol (rubbing alcohol) for good measure.   Remove all your clothes that have come in contact with the plant and wash them with soap and water. Be especially careful with your shoes, many people pick up the oils on their hands while removing their shoes. When in doubt, wash with soap and water. Some common myths include the idea that it is contagious or that scratching spreads it; these derive from the fact that it can take several days for the rash to appear and that various parts of your body have thicker or thinner skin that reacts differently to the exposure. It is also a myth (and a dangerous one) that eating poison ivy gives you immunity! There are animals like deer and sheep that can eat it with no ill effects, but humans are not in that group. You can still get contact dermatitis from a dead poison ivy plant, the urushiol can still pack a punch for many years after the plant has died. It is also important to remember that the oils can stay on tools long after they are put away, so wash tools and gloves if you suspect they have been in contact with poison ivy.

If all this fails and you get the tell-tale blisters or red streaks from contact dermatitis, there are several things you can do as a treatment. You can apply a topical corticosteroid (over-the-counter brands such as Cortaid and Lanacort), or take an over-the-counter antihistamine (such as Benadryl) to relieve the itching. Prescription cortisone can stop the reaction, but only if it is taken soon after exposure. Other topical products that can soothe itching are calamine lotion, zinc oxide ointment, baking soda paste (3 teaspoons baking soda and 1 teaspoon water), or an oatmeal bath (Aveeno). Cold compresses can help and I often use clear Caladryl and Ivy Dry. If you are camping and you touch poison ivy put deodorant stick on it right away if you aren’t near water. This will prevent the oil from spreading anywhere else. If you don’t have any other soap available, trying washing off with dish soap (just as it cuts the grease off your dishes, it effectively cuts the urushiol oil off the skin).

You can use a weed killer in areas a good distance from wetlands that contains glyphosphate to kill the plants, but most weed killers that work on PI are not selective. The best way to remove it is to pull it (roots and all) but you’ll want to wear long pants and a long sleeve shirt and gloves and wash your clothes in hot soapy water afterwards. Never burn the plant as it vaporizes the urushiol and can give you a severe reaction. Plants will die after they are pulled. Although it is listed as a noxious weed in many states, poison ivy is not an invasive plant and has been in North America for millennia.

This web site about poison ivy called primary purpose is to help newbies identify this leafy menace. Two or three times a year, I give a talk entitled the “Effects of Climate Change on Nantucket” and the biggest groans come from the audience when they see the slide that illustrates the adverse effects of increased carbon dioxide (CO2) in the atmosphere in relationship to plants. You would think, more CO2, means more fuel for plants, and that must be all good, right? Well, some plants are much more adept at reacting quickly and decisively to excess CO2. And one of the all-time most likely to succeed in an ever increasing CO2 atmosphere is, ding ding ding, you guessed it: poison ivy. Researchers from the Nicholas School of the Environment at Duke University conducted an experiment that made headlines around the world. Jacqueline Mohand and her co-authors (James S. Clark and William H. Schlesinger) conducted the study over six years at the Free-Air Carbon Dioxide Enrichment (FACE) site in Duke Forest, where carbon dioxide is dispersed into the air at levels similar to those predicted to occur on Earth in 2050. They found that poison ivy vines in the CO2-rich area grew 149 percent faster and produced a concentration of urushiol that was 153 percent higher than vines grown in control plots Super powered poison ivy is yet another reason to dislike climate change!

At the weekly Sustainable Nantucket Farmers and Artisans Market I picked up two items to add to my arsenal of poison ivy fighting potions: a jewelweed tincture and some jewelweed soap. Jewel Weed prefers moist, alluvial areas and the juice from the broken stem of the plant is a folk remedy for poison ivy exposure. Jewelweed is an annual North American plant also known as “touch me not” for their projectile seeds. It usually grows near water or in shallow ponds near areas where Poison Ivy grows (extremely conveniently). The species most often associated with rash relief is Impatiens capensis, also known as the Orange Jewelweed, Common Jewelweed, Spotted Jewelweed, Spotted Touch-me-not, or Orange Balsam. You can find it at the Nantucket Field Station, near our many lovely examples of poison ivy. We’ll be glad to help you avoid one, and explore the other.

Articles by Date from 2012