Poison ivy is a woody vine, shrub or ground cover that can be encountered almost anywhere in our region. You will definitely find plenty of it in woodsy areas, but it could just as easily show up in your urban garden or a raised planting bed. Its distribution includes the entire U.S., southern
Canada and Mexico. There are varieties of it throughout the world.
Interestingly, this plant is a member of the “Anacardiaceae,” or cashew family. While most cashew representatives are located in tropical or sub-tropical areas, in North America this family is represented by poison ivy, poison oak, the sumacs (including poison sumac) and the Florida poison tree. In addition to poison ivy, this series will discuss poison oak and poison sumac.
THE POISON IN THE IVY
It’s too bad that poison ivy is as far-ranging as it is, since its active agent, Urushiol (pronounced oo-roo-shee-ohl), is present in all parts of the plant, especially the sap, and can be easily released and encountered in the wild. Almost all people (well, 85%, according to the FDA) are sensitive to Urushiol. Although the human immune system will generally not react to Urushiol upon the first exposure to it, subsequent exposures will usually result in the outbreak of an itchy rash within 12 to 48 hours, followed by nasty blisters that eventually ooze and erupt. The oozing blisters, by the way, are not contagious and can not spread the reaction to other parts of the body. Any new lesions that appear well after the primary ones represent less sensitive areas where the Urushiol was deposited. The rash, blisters and itch normally disappear in 14 to 20 days without treatment.
People vary significantly in sensitivity to Urushiol. Some people have little problem with it, only getting minor rashes after significant exposure. Others, not as fortunate, may suffer severe allergic reactions. Sensitivity can also vary over a person’s lifetime. It has been shown, for instance, that people who may be unaffected by light Urushiol exposure early in life can become sensitized with repeated exposures later on. Other animals are not sensitive to Urushiol, so although Fido can bring it to you on his shiny coat, he can’t suffer it himself. The sad ironic reality about human exposure to Urushiol is this: in and of itself, Urushiol is a harmless substance. It’s the unique human immune response to it that causes all the problems. It’s like Pogo said, “We have met the enemy, and he is us!”
The clinical name for the skin irritation caused by poison ivy is “Rhus Dermatitis,” which usually starts as itching, then proceeds to small blisters at the exact spot of exposure within a few hours. The strength of the exposure, as well as the sensitivity of the person exposed, will determine the severity of the reaction. Most people are exposed to poison ivy, which is a fragile plant anyway, when they inadvertently rub up against and bruise a leaf or vine. The tiny bit of Urushiol that drains onto the skin begins the reaction process. Unfortunately, Urushiol can cling to shoes, clothing, tools, balls, pets and virtually anything else, resulting in exposure long after a person has left the poison ivy habitat. In a dry environment the substance can remain viable for decades, but even if the environment is warm and moist, the Urushiol can still cause a reaction a year later. Because we tromp through a lot poison ivy seeking caches, our shoes become a prime carrier if the Urushiol is not washed off or brushed off by other weeds and plants during our bushwhacking activities.
Urushiol is absorbed into the skin within five to 15 minutes and combines molecularly with certain proteins in the body. If, upon exposure or very shortly thereafter, the Urushiol is washed off (preferably with dishwashing soap and water), the consequences can be mitigated quite a bit or eliminated altogether. Unfortunately, cachers are rarely near a sink or water or soap when they are traipsing through a forest. The best strategy is to learn to recognize the vectors of Urushiol, like poison ivy, and steer clear of them. We will discuss identification of poison ivy shortly, but first, consider these facts about Urushiol:
Only one nanogram (billionth of a gram) is needed to cause a rash. The average exposure is 100 nanogams.
Five hundred people could itch from the amount covering the head of a pin, while one-quarter ounce would cause a reaction in every person on earth.
Specimens of Urushiol several centuries old have been found to cause dermatitis in sensitive people.
The name "Urushiol is derived from the Japanese name for lacquer. When the Japanese restored the gold leaf on the Temple of Kyoto, they painted the Urushiol lacquer on it to preserve and maintain the gold. (It could have been a good deterrent against thievery, too!)
Urushiol reactions are the most common form of allergy in the U.S.
IDENTIFICATION
Since avoidance of poison ivy is the best way to avoid exposure to Urushiol, how do we identify it?
As previously mentioned, poison ivy can appear in a number of different forms. As a vine, it produces an abundance of hairy-looking aerial roots and can grow high up on trees, walls, fences or anything else that can support it. In this form it can reach its greatest size. We’ve all seen those hairy, arm-sized vines growing up the sides of large trees. But be aware that it can also trail along the ground as a vine, usually much smaller in size, in which case it may appear to be something innocuous like a root. Don’t grab a poison ivy vine for support when you’re climbing up a slope, thinking it’s a root from a nearby tree!
As a free-standing shrub, specimens can be very small, growing in the open with only one stem and a few side branches. On the other hand, poison ivy’s shrub form can be very large, easily over 10’ tall and approaching tree-like status. This latter size is often confused with poison oak, a related hazard we’ll discuss in the next installment.
Finally, as a ground cover poison ivy can creep across the ground and create a knee-high thicket of foliage that can easily get caught in a hiking shoe’s loose toe-guard, thereby resulting in a fall. Yikes! Did I just land in poison ivy?
Fortunately, the leaves of poison ivy, which are similar in all three forms, are the basic key to identification in the field. (The bad news is that poison ivy leaves are not strictly uniform. They are close enough, however, that positive identification should not be a problem.) Keep in mind, though, that while the old adage, “Leaves of three, let it be!” will steer you clear of poison ivy, that old saying will also have you jumping away from many other innocuous plants you’ll encounter on your treks. Lest you become a human jumping bean getting spooked at every turn, let’s see if we can’t put a little more definition into that age-old bromide.
Poison ivy has “compound” leaves. This means that each leaf is made up of distinct parts, called leaflets. The key to identifying poison ivy is to know that one leaflet (and the largest of the three) is positioned at the end of the stalk, with the other two leaflets situated opposite each other below the central large leaflet. The two lower leaflets have much shorter stalks than the central leaflet. This is called a trifoliate pattern. Also, and this is especially true in our region, the shape, color and texture of the leaflets are highly variable. (You will also note that the central stalk will often have a number of small, bristly aerial roots, especially noticeable on vines.) In our area I would guess that about 60% of the poison ivy has smooth leaf margins, with the remaining 40% having “toothed” margins or lobes. To reiterate: the key factors in identifying poison ivy are the larger central leaflet with its larger stalk and the two opposite somewhat smaller leaves on substantially smaller stalks. If you remember these features you will be able to distinguish poison ivy from any other plant.
A word on leave color: In spring it’s common to see poison ivy emerge with a reddish leaf that quickly turns green. Similarly, in fall the leaves will often become reddish late in their growth cycle before dying off and turning yellow or dirty red. In the midst of their growth cycle, the leaves of poison ivy can range from dull flat green in color through bright green. Also, while most poison ivy leaves are fully formed and spread out during the plant’s growing season, it’s not uncommon to find some plants, particularly small shrubs, with droopy, dark green leaves that appear to have a waxy hue to them. This plant does give us a number of different looks!
Another way to identify poison ivy is through its fruit. During the summer months poison ivy produces grapelike clusters of tiny white, pumpkin-like seeds with an off-white or pale yellow rind. Eventually, the rind flakes off and exposes the seed. Well before this happens, however, the rind-bound seeds are feasted upon by a variety of birds, including flickers and woodpeckers, sapsuckers, thrushes, pheasants and quail. Songbirds also eat the fruit during their fall migrations and during the winter when other foods are scarce. The rind provides the birds with nourishment, while the seeds usually pass through the birds’ gut unharmed. In this way, birds act as agents in the spread of poison ivy.
Finally, if you happen to brush up against what you believe could be poison ivy (or oak and sumac, for that matter), here’s a test you can perform virtually anywhere AFTER you thoroughly wash and rinse the exposed area. The test will take about 30 minutes and require a sheet of white paper (like copy paper) and a pair of gloves (preferably PVC-coated). Wearing the gloves for protection, break off a full leaf (as opposed to just one of the leaf’s leaflets) of the suspect plant where it meets the main stem. Put the broken end of the leaf against the paper to create a “dot” of the sap. Wait 30 minutes. If this plant is one of the “big three” containing Urushiol, the dot will oxidize and turn black within that time.
POISON IVY LOOK-ALIKES
Please note the accompanying photos of some other plants that are often confused with poison ivy. These include fragrant sumac, box elder, Virginia creeper, blackberry and wild strawberry. Like poison ivy, fragrant sumac is trifoliate. It grows in dense thickets up to seven feet tall. Box elder has three to seven leaflets on each leaf. Unlike poison ivy, its leaves will be opposite each other on the main stem. The Virginia creeper leaf has three to five leaflets (usually five) and, to my thinking, has little resemblance to poison ivy. What IS similar, however, is its large vine. Blackberry will show three leaves, but they are always very serrated and the stalk of the central leaflet is much shorter. Also the stems and stalks are loaded with small thorns. Wild strawberry creeps low to the ground, and its middle leaflet does not have a longer stalk than the other two. Since pictures of these imposters will be included with this article, no further attempt will be made to describe them in this article.
TREATMENT OF EXPOSURE
If you are unfortunate enough to have developed a poison ivy rash, there are several ways to treat it, depending on the severity of the reaction. For mild cases, wet compresses or soaking in cool water may be effective. Oral antihistamines can also relieve itching. A variety of over-the-counter topical corticosteroids (commonly referred to as hydrocortisones under brand names like Cortaid and Lanacort) are safe and effective in reducing the itch of poison ivy. A couple other non-prescription topical products reputed to be effective are Zanfel, Itch-X and Tecnu. An itch-relieving spray given good marks is Cahladril.
In a recent real-world inquiry into effective non-prescription poison ivy treatments available to the general public, the highest-ranked remedies were Zanfel, hot water, swimming pool (!) and jewelweed, followed by a host of home cures. According to Geode Hunters, by the way, “the inside of banana peels helps in relieving the itching and dries out the skin. Lye soap also helps dry out the skin…. Tecnu is the winner, though. Even after a long day of caching in the woods, I find it effective. I use it in the shower, and it seems to do the job.” (Jewelweed, long-known as a home cure, has significant scientific validation. It will be discussed in length in the next installment.)
For severe cases, prescription topical corticosteroid drugs can halt the reaction, but only if treatment begins within a few hours of exposure. Once the blisters form, topical treatments lose efficacy. At this point it would be wise to visit a dermatologist. He/she will be able to judge the severity of the reaction and may prescribe oral or injected corticosteroids. Predisone is generally the preferred recourse in severe cases, as well as a number of prescription topicals that are also generally formulated with corticosteroids.
There are a number of OTC products that help dry up blisters. In addition to the ones mentioned by Geode Hunters, these include aluminum acetate (Burrows solution), baking soda, Aveeno (oatmeal bath), aluminum hydroxide gel, calamine, kaolin, zinc acetate, zinc carbonate and zinc oxide. Currently, there are no FDA-approved desensitization, vaccination or barrier products available, although many have been studied. Right now most experts agree that one old adage DOES apply to poison ivy exposure. You’ve heard it before: “An ounce of prevention is worth a pound of cure.” In other words, avoid it if you can. For geocachers, that means learning what it is and stepping around it.
